Supported catalyst with mixed lanthanum and other rare earth oxides

ABSTRACT

An improved supported catalyst containing mixed strontium and other alkaline earth oxides deposited on a sintered low surface area porous catalyst carrier (or support) precoated with mixed lanthanum and other rare earth oxides, represented by the formula: 
     
         A.sub.a SrO.sub.b (x)/R.sub.c LaO.sub.d (y)/S, 
    
     wherein, A is alkaline earth element selected from Be, Mg, Ca, Ba or a mixture thereof; Sr is strontium; O is oxygen; R is rare earth element selected from Ce, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu or a mixture thereof; La is lanthanum; S is catalyst support selected from sintered low surface area porous refractory inert solids comprising of alumina, silica, silica-alumina, silicon carbide, zirconia, hafnia or a mixture thereof; a is A/Sr mole ratio in the range of about 0.01 to about 10; b is number of oxygen atoms needed to fulfill the valence requirement of alkaline earth elements (A a  Sr); c is R/La mole ratio in the range of about 0.01 to about 10; d is number of oxygen atoms needed to fulfill the valence requirement of rare earth elements, (R c  La); y is weight percent loading of rare earth oxides (R c  LaO d ) precoated on the support in the range of about 0.5 wt % to about 50 wt % and x is wt % loading of alkaline earth oxides (A a  SrO b ) deposited on the precoated support in the range of about 0.4 wt % to about 40 wt %.

This invention relates to an improved supported catalyst prepared by thedeposition of mixed strontium and other alkaline earth oxides on asintered low surface area porous catalyst carrier (i.e. support)precoated with mixed lanthanum and other rare earth oxides. Catalystprepared by the process of the present invention is useful for theoxidative conversion of methane or natural gas to ethylene, ethane andhigher hydrocarbons (C₃ + hydrocarbons) and also for the oxidativedehydrogenation of ethane or C₂ -C₄ alkanes.

More particularly, the invention relates to a process for thepreparation of an improved supported catalyst with mixed lanthanum andother rare earth oxides. This invention particularly relates to aprocess for the oxidative conversion of methane or natural gas toethylene and higher hydrocarbon and for the oxidative conversion ofethane or C₂ -C₄ paraffins to ethylene and higher olefins (propylene andbutylenes) employing the improved supported catalyst diluted with aninert solid.

The process of manufacture of the the improved catalyst could be used bycatalyst manufacturers, and by the producers of higher hydrocarbons(i.e. C₂ +-hydrocarbons) from methane and of ethylene and other lowerolefins (i.e. propylenes and butylenes) from methane, natural gas,ethane-propane mixtures, propane and butanes.

BACKGROUND OF THE INVENTION

The prior art, use of a number of catalysts in the oxidative coupling ofmethane to C₂ -hydrocarbons (i.e. ethane and ethylene) and in theoxidative dehydrogenation of C₂ -C₄ alkanes is known.

At present, ethylene, which is a keystone to the petrochemicals, fromlight paraffins (c₂ -C₄ paraffins) is produced commercially from lightparaffins (C₂ -C₄ paraffins) by a well established process based on thethermal cracking of ethane or C₂ -C₄ paraffins at 750°-1000° C. Thecracking process is highly endothermic and involves coke deposition (L.Kniel, O. Winter and K. Stork in Chemical Industries, Vol. 2 "Ethylene:Key-stone to the Petrochemical Industry", Marcel Dekkor, Inc., New Yorkand Basel). Typical results given in the above reference indicate thatat 50% and 60% conversion of ethane with 83.3% and 80.0% selectivity forethylene, respectively, could be obtained by the thermal cracking ofethane.

The process for production of ethylene, based on thermal cracking oflight paraffins have following limitations: (1) They are highlyendothermic and hence are energy intensive, (2) They involve extensivecoke deposition inside the pyrolysis reactor tubes, thus causingincrease in pressure drop and frequent break downs.

Catalytic processes based on oxidative dehydrogenation of ethane orlight paraffins are also known in the prior art. A number of catalystscontaining low melting compounds such as alkali metal compounds, metalhalides and other low melting metal oxides are known for the oxidativedehydrogenation of ethane or lower alkanes (Ref. Eastman and Kolts, U.S.Pat. No. 4,310,717 (1982); Eastman, U.S. Pat. No. 4,368,346 (1983);Eastman and Kimble, U.S. Pat. No. 4,450,313 (1985); Kimble, U.S. Pat.No. 4,476,344 (1984); Eastman et. al., U.S. Pat. No. 4,497,971 (1985);Jpn. Kokai Tokyo Koho JP 61,282,322 (1986); Kolts and Guillory, Eur.Pat. Appl EP 205,765 (1986). Because of the presence of the low meltingor volatile component, these catalysts are deactivated during theprocess due to the loss of active components from the catalyst byevaporation at hot spots and/or due to the catalyst sintering.

Methane is a major constituent of natural gas and also of bio-gas.Processed natural gas typically comprises a major amount of methane andminor amounts of ethane, propane, butanes, CO₂ and nitrogen and verysmall amount of pentanes. Methane or natural gas is used principally asa source of heat in commercial, industrial and residential services andalso a source of hydrogen for the fertilizer industries and syngas (COand H₂) for the production of methanol and in the Fischer-Tropcshsynthesis. World reserves of natural gas are constantly being upgradedand more and more natural gas is being discovered than oil. Because ofthe problem associated with transportation of a very large volume ofnatural gas, most of the natural gas produced particularly at remoteplaces is flared. This causes not only a wastage of valuable energy butalso causes a global warming due to release of large amount of CO₂ inthe atmosphere. If energy efficient commercially feasible processes wereavailable for converting methane or natural gas into value addedproducts like ethylene and other lower olefins, which can be convertedto easily transportable petrochemicals and liquid hydrocarbons by knownprocesses, this can have far reaching economic impact and also theexploration of more gas-rich fields could greatly increase the naturalgas reserves.

Researchers at Atlantic Richfield Co. (U.S.A.) patented a series ofsupported reducible metal oxides, such as oxides of Mn, Bi, Ge, In, Pb,Sb, Sn and Pr with or without alkali metals supported on SiO₂ or MgO, ascatalysts for the oxidative conversion of methane to ethane andethylene, utilising a so-called "Redox" approach, which use latticeoxygen from the catalyst to perform the oxidative coupling of methane toC₂ -hydrocarbons at about 800° C. and gas hourly space velocity of about860 h⁻¹ (Ref. Jones and Co-workers, J. Catal., 103, 302-319 (1987);Jones et.al., Energy and fuels, 1, 12-16 (1987); Jones et.al., U.S. Pat.Nos. 4,443,644; 4,443,645; 4,443,646; 4,443,647; 4,443,648; 4,443,649;4,499,322; 4,444,984 (1984); 4,495,347; 4,517,398 (1985); Withers, et.al, U.S. Pat. No. 4,634,800 (1987); Sofranko and Jones, U.S. Pat. No.4,544,784 (1987). These catalysts are based on reducible metal oxidesand are used in a stoichiometric fashion by atlernatively exposing themto an oxidising atmosphere and then to methane in the absence of freeoxygen. The main drawbacks of the processes using reducible metal oxidesas catalysts following "Redox" approach in the oxidative conversion ofmethane are as follows:

(i) The "Redox" operation is very complicated and requires a complicatedreactor consisting of physically separate zones for a methane contactingstep and for an oxygen contacting step, with an arrangement forrecirculating the catalyst between two zones.

(ii) Because of the "Redeox" operation and requirement of lower spacevelocity of methane to achieve reasonable methane conversion, theproductivity of ethane and ethylene is very low.

(iii) The "Redox" catalyst without containing alkali metals showed verypoor activity and selectivity in the oxidative methane coupling process;whereas the alkali metal containing catalysts showed good activity andselectivity but the alkali metal containing catalysts are expected to bedeactivated fast because of the evaporation of alkali metals and alsodue to the catalyst sintering during the high temperature processoperation.

A number of alkali metal promoted catalysts, such as alkali metalcontaining alkaline earth metal oxides, group III and IV metal oxidesand the catalysts containing low melting metal compounds have beendescribed for the oxidative conversion of methane to C₂ -hydrocarbons inpresence of free oxygen (Ref. Kimble and Kolts, Chemtech, 501 (1987);Baerns et. al., U.S. Pat. No. 4,608,449 (1986); Leyshon et.al., U.S.Pat. No. 4,801,762 (1989); Devries et.al., U.S. Pat. No. 4,814,538(1989); Kimble et. al., U.S. Pat. No. 5,087,787 (1992); Lunsford andHinson, U.S. Pat. No. 5,041,405 (1991). The main drawback of the use ofthese catalysts in the oxidative conversion of methane to higherhydrocarbons are that the catalysts are deactivated during the processbecause of the loss of active components from the catalyst byevaporation and also due to sintering of the catalysts during theiroperation in the high temperature process.

Recently in U.S. Pat. No. 4,822,944 (1989), Brazdil Jr., et.al. havedisclosed a novel oxidative methane coupling catalyst, having meltingpoints above 900° C., represented by the formula: SrLa_(n) O_(x),wherein n is a number in the range of about 0.1 to about 100, and x isthe number of oxygens needed to fulfil the valence requirements of theother elements. The catalyst is prepared generally by mixing an aqueoussolution of compounds containing the metal components, forming aprecipitate, drying this precipitate and calcining to produce desirablephysical properties. Although, the catalyst disclosed by Brazdil Jr.et.al. has high thermal stability against evaporation of active catalystcomponent during the oxidative methane coupling process occurring athigh temperature (at about 900° C.), the catalyst shows poor activityand also poor selectivity in the oxidative coupling of methane; forexample, at the catalyst temperature of 915°-916° C. and the gas hourlyspace velocity of 23,570 cm³.g⁻¹.h⁻¹, the methane conversion, C₂ + yieldand C₂ + selectivity are 14.2-14.6%, 8.7-9.1% and 61.2-62.8%respectively. Further the catalyst operates in the oxidative methanecoupling process at high temperature about 900° C. and yet shows verypoor catalytic activity. Hence, there is a need to develop an improvedcatalyst which is not only thermally stable at high temperature but alsohighly active and selective in the oxidative coupling of methane tohigher hydrocarbons.

The price of methane or natural gas is high and it is increasingday-by-day because of energy crisis. Hence, the oxidative conversion ofmethane or natural gas to ethylene will be economically feasible only ifthe selectivity and productivity for ethylene in the conversion processare high and when process is operated continuously for a long periodwithout catalyst deactivation and/or fouling due to a loss of catalyticactivity or mechanical strength. In the oxidative conversion of methaneto ethylene, two methane molecules are coupled to form ethane which isthen dehydrogenated to ethylene. Therefore, in order to make catalyticoxidative methane-or natural gas-to-ethylene conversion processeconomically feasible and/or competitive to the conventional processesused for the production of ethylene, there is a need to use an improvedcatalyst, preferably an improved supported catalyst, which is thermallyand hydrothermally stable at the process operating conditions, has highmechanical strength and has high activity and productivity with veryhigh selectivity not only in the oxidative coupling of methane to ethanebut also in the oxidative dehydrogenation of ethane to ethylene, andalso has long life in the process.

The present invention is directed to overcome the limitations anddrawbacks of the earlier catalysts thereby providing a novel improvedsupported catalyst.

The objective of the invention is to provide an improved supportedcatalyst comprising strontium and rare earth oxides deposited on asintered low surface area porous catalyst carrier (or support).

Another objective of the invention is to provide an improved supportedcatalyst having higher activity, selectivity and efficiency (orproductivity) in the oxidative coupling of methane to higherhydrocarbons (C₂ +-hydrocarbons) in the presence of free oxygen withoutcatalyst deactivation or fouling during the process.

The other objective of the invention is to provide an improved supportedcatalyst having high activity, selectivity and productivity in theoxidative conversion of natural gas to ethylene and other lower olefin(i.e. propylene and butylenes) and in the oxidative dehydrogenation ofethane and other lower alkanes (i.e. propane and butanes) to thecorresponding olefin and also has high thermal and hydrothermalstability during the operation of these oxidative methane, natural gasand lower alkanes conversion processes.

Another objective of the present invention is to provide a process forthe manufacture of an improved supported catalyst.

Another objective of the present invention is to provide an improvedsupported catalyst which operates at a temperature below 900° C. withhigher activity, selectivity and productivity useful for the oxidativecoupling of methane to higher hydrocarbons.

Another objective of the present invention is to provide highly energyefficient and safe process for oxidative conversion of methane ornatural gas to ethylene, ethane and higher hydrocarbons and for theoxdative dehydrogenation of ethane of C₄ -C₄ alkanes to ethylene andhigher olefins employing the improved catalyst of this invention.

SUMMARY OF THE INVENTION

This invention provides an improved supported catalyst, containing mixedstrontium and other alkaline earth oxides deposited on a sintered lowsurface area porous catalyst carrier (or support) precoated with mixedlanthanum and other rare earth oxides, represented by the formula:

    A.sub.a SrO.sub.b (x)/R.sub.c LaO.sub.d (y)/S,

wherein, A is alkaline earth element selected from Be, Mg, Ca, Ba or amixture thereof; Sr is strontium; O is oxygen; R is rare earth elementselected from Ce, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu or amixture thereof; La is lanthanum; S is catalyst support selected fromsintered low surface area porous refractory inert solids comprising ofalumina, silica, silica-alumina, silicon carbide, zirconia, hafnia or amixture thereof; a is A/Sr mole ratio in the range of about 0.01 toabout 10; b is number of oxygen atoms needed to fulfil the valencerequirement of alkaline earth elements (A_(a) Sr); c is R/La mole ratioin the range of about 0.01 to about 10; d is number of oxygen atomsneeded to fulfil the valence requirement of rare earth elements, (R_(c)La); y is weight percent loading of rare earth oxides (R_(c) LaO_(d))precoated on the support in the range of about 0.5 wt % to about 50 wt %and x is wt % loading of alkaline earth oxides (A_(a) SrO_(b)) depositedon the precoated support in the range of about 0.4 wt % to about 40 wt%.

In accordance with the present invention there is also provided aprocess for the preparation of an improved supported catalyst,containing mixed strontium and other alkaline earth oxides deposited ona sintered low surface area porous catalyst carrier (or support)precoated with mixed lanthanum and other rare earth oxides representedby the general formula:

    A.sub.a SrO.sub.b (x)/R.sub.c LaO.sub.d (y)/S.

The present invention also provides an important process for theoxidative conversion of methane or natural gas to enthylene, ethane andhigher hydrocarbons using the improved support catalyst defined above.

The present invention also provides an improved process for theoxidative conversion of ethane or C₂ -C₄ paraffins to ethylene andhigher olefins (propylenes and butylenes). All the above improvedprocess of this invention involve simultaneous occurrence of exothermicand endothermic hydrocarbon conversion reaction thus making them mostenergy efficient and safe to operate requiring little or no externalenergy.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the present invention there is also provided aprocess for the preparation of an improved supported catalyst,containing mixed strontium and other alkaline earth oxides deposited ona sintered low surface area porous catalyst carrier (or support)precoated with mixed lanthanum and other rare earth oxides, representedby the general formula:

    A.sub.a SrO.sub.b (x)/R.sub.c LaO.sub.d (y)/S,

wherein, A is alkaline earth element selected from Be, Mg, Ca, Ba or amixture thereof; Sr is strontium; O is oxygen; R is rare earth elementselected from Ce, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu or amixture thereof; La is lanthanum; S is catalyst support selected fromsintered low surface area porous refractory inert solids comprising ofalumina, silica, silica-alumina, silicon carbide, zirconia, hafnia or amixture thereof; a is A/Sr mole ratio in the range of about 0.01 toabout 10; b is number of oxygen atoms needed to fulfil the valencerequirement of alkaline earth elements (A_(a) Sr); c is R/La mole ratioin the range of about 0.01 to about 10; d is number of oxygen atomsneeded to fulfil the valence requirement of rare earth elements, (R_(c)La); y is weight percent loading of rare earth oxides (R_(c) LaO_(d))precoated on the support in the range of about 0.5 wt % to about 50 wt %and x is wt % loading of alkaline earth oxides (A_(a) SrO_(b)) depositedon the precoated support in the range of about 0.4 wt % to about 40 wt%, useful for the oxidative coupling of methane to higher hydrocarbons(i.e. C₂ +-hydrocarbons), oxidative conversion of natural gas toethylene and other lower olefins (propylene and butylenes) and for theoxidative dehydrogenation of ethane or C₄ -C₄ alkanes to correspondingolefins, in the presence of free oxygen, which comprises:

(i) precoating of the surface of the support by the deposition of R_(c)LaO_(d) on it by impregnating or coating the support with the mixedcompounds of lanthanum and other rare earth elements, represented by thegeneral formulae: LaY_(g) and RY_(g), respectively, wherein La islanthanum, R is rare earth element selected from Ce, Nd, Pm, Sm, Eu, Gd,Tb, Dy, Ho, Er, Tm, Yb, Lu or a mixture thereof, Y is an anion selectedfrom nitrate, acetate, formate, oxalate, hydroxide, oxide and carbonateanion, g is number of Y needed to fulfil the valence requirement oflanthanum and other rare earth elements in their compounds, which ondecomposition converts into oxide form, with R/La mole ration, c, in therange of about 0.01 to about 10 and in quantities sufficient to obtain aloading of R_(c) LaO_(d) on support in the range of about 0.5 wt % toabout 50 wt %, by the known incipient wetness impregnation, wetimpregnation or coating methods, followed by drying the wet mass byheating it in air or under vacuum first slowly at about 60° C. for about5 h and then at about 110° C. for about 2 h, and then decomposing thedried mass by heating it in air or inert gas or under vacuum at atemperature in the range of about 400° C. to about 700° C. for a periodin the range of about 0.5 h to about 15 h and finally calcining it at atemperature in the range of about 600° C. to about 1200° C. in air orinert gas or under vacuum for a period in the range of about 0.2 h toabout 20 h to obtain the support precoated with the rare earth oxides(R_(c) LaO_(d)), and (ii) deposition of A_(a) SrO_(b) on the surface ofthe precoated support by impregnating or coating it with mixed compoundsof strontium and other alkaline earth elements, represented by thegeneral formulae: SrX_(f) and AX_(f), respectively, wherein Sr isstrontium, A is alkaline earth element selected from Be, Mg, Ca, Ba or amixture thereof, X is an anion selected from nitrate, acetate, formate,oxalate, oxide, carbonate and hydroxide anion, f is a number of X neededto fulfil the valence requirement of strontium and other alkaline earthelements in their compounds, which on decomposition convert into theoxide form, with A/Sr mole ration, a, in the range of 0.01 to about 10and in quantities sufficient to obtain a loading of A_(a) SrO_(b) on theprecoated support in the range of about 0.4 wt % to about 40 wt % by theknown incipient wetness impregnation, wet impregnation or coatingmethods, followed by drying slowly the wet catalyst mass by heating itin air or under vacuum at about 60° C. for about 5 h and further atabout 110° C. for about 2 h, and then decomposing the dried catalystmass by heating it in air or inert gas or under vacuum at a temperaturein the range of about 400° C. to about 700° C. for a period in the rangeof about 0.5 h to about 15 h and finally calcining it in air, inert gasor under vacuum at a temperature in the range of about 600° C. to about1200° C. for a period in the range of about 0.2 h to about 20h. Thesupport used in the preparation of an improved catalyst of thisinvention is in the form of granules (or aggregates) of size in therange of about 0.1 mm to about 8 mm or in the form of spheres,cylindrical pellets, rings, saddles or star of size or diameter in therange of about 1 mm to about 15 mm, or in the form of monolith, and hassurface area, pore volume and porosity in the range from about 0.001m².g⁻¹ to about 5.0 m².g⁻¹, about 0.02 cm³.g⁻¹ to about 0.6 cm³.g⁻¹ andabout 5% to about 75% respectively.

In accordance with the present invention there is also provided aprocess for the oxidative conversion of methane or natural gas toethylene, ethane and higher hydrocarbons, operating in a most energyefficient and safe manner by allowing the endothermic hydrocarboncracking reactions to occur simultaneously with the exothermichydrocarbon oxidation reactions in a fixed diluted-catalyst bed reactor,using an improved supported catalyst, containing mixed strontium andother alkaline earth oxides deposited on a sintered low surface areaporous inert support precoated with mixed lanthanum and other rare earthoxides, represented by the general formula:

    A.sub.a SrO.sub.b (x)/R.sub.c LaO.sub.d (y)/S,

wherein, A is alkaline earth element selected from Be, Mg, Ca, Ba or amixture thereof; Sr is strontium; O is oxygen; R is rare earth elementselected from Ce, Nd, Pm, Sm, Eu, Gd, Tb, Dy, HO, Er, Tm, Yb, Lu or amixture thereof; La is lanthanum; S is catalyst support selected fromsintered low surface area porous refractory inert solids comprising ofalumina, silica, silica-alumina, alumina, silicon carbide, zirconia,hafnia or a mixture thereof; a is A/Sr mole ratio in the range of about0.01 to about 10; b is number of oxygen atoms needed to fulfil thevalence requirement of alkaline earth elements (A_(a) Sr); c is R/Lamole ratio in the range of about 0.01 to about 10; d is number of oxygenatoms needed to fulfil the valence requirement of rare earth elements,(R_(c) La); y is weight percent loading of rare earth oxides (R_(c)LaO_(d)) precoated on the support in the range of about 0.5 wt % toabout 50 wt wt % and x is wt % loading of alkaline earth oxides (A_(a)SrO_(b)) deposited on the precoated support in the range of about 0.4 wt% to about 40 wt % which comprises:

(a) mixing oxygen with methane or natural gas at ambient temperature orbelow its ignition temperature.

(b) preheating steam and the mixture of oxygen and methane or naturalgas to a temperature between about 550° C. and about 850° C.,

(c) admixing said preheated steam with said preheated mixture of oxygenand methane or natural gas,

(d) passing continuously the resulting admixture feed over the saidimproved supported catalyst defined above diluted with the said inertsolid (i.e. catalyst diluent) with the volume ratio of catalyst diluentto catalyst between about 0.5 and about 500 in a fixed reactor,maintaining the mole ratio of organic carbon (i.e. carbon inhydrocarbon) to oxygen and steam in said admixture feed between about 3and about 90 and between about 0.1 and about 100, respectively, a gashourly space velocity of said admixture feed between about 5×10³ cm³ g⁻¹catalyst.h⁻¹ and about 1×10⁶ cm³.g⁻¹ catalyst. h¹, a reactiontemperature between about 700° C. and about 1000° C. and a pressurebetween about 1 atm and about 50 atm and separating the components ofeffluent product gases by known methods and recycling the unconvertedreactants.

In accordance with the present invention there is also provided aprocess for the oxidative conversion of ethane or C₂ -C₄ paraffins toethylene and higher olefins (propylene and butylenes), operating in amost energy efficient and safe manner by allowing the endothermichydrocarbon cracking reactions to occur simultaneously with theexothermic hydrocarbon oxidation reactions in a fixed diluted-catalystbed reactor in the presence of free oxygen and steam, using the improvedsupported catalyst, containing mixed Strontium and other alkaline earthoxides deposited on a sintered low surface area porous inert supportprecoated with mixed lanthanum and other rare earth oxides, representedby the general formula:

    A.sub.a SrO.sub.b (x)/R.sub.c LaO.sub.d (y)/S,

wherein, A is alkaline earth element selected from Be, Mg, Ca, Ba or amixture thereof; Sr is strontium; O is oxygen; R is rare earth elementselected from Ce, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu or amixture thereof; La is lanthanum; S is catalyst support selected fromsintered low surface area porous refractory inert solids comprising ofalumina, silica, silica-alumina, silicon carbide, zirconia, hafnia or amixture thereof; a is A/Sr mole ratio in the range of about 0.01 toabout 10; b is number of oxygen atoms needed to fulfil the valencerequirement of alkaline earth elements (A_(a) Sr); c is R/La mole ratioin the range of about 0.01 to about 10; d is number of oxygen atomsneeded to fulfil the valence requirement of rare earth elements, (R_(c)La); y is weight percent loading of rare earth oxides (R_(c) LaO_(d))precoated on the support in the range of about 0.5 wt % to about 50 wtwt % and x is wt % loading of alkaline earth oxides (A_(a) SrO_(b)) onthe precoated support in the range of about 0.4 wt % to about 40 wt %,the said catalyst is diluted with an inert porous or non-porousrefractory solid comprising of fused or highly sintered alumina,magnesia, silica, silica-alumina, silicon carbide, calcium oxide,zirconia, hafnia or a mixture thereof, the process comprises:

(a) mixing of oxygen or air with enriched oxygen and ethane or C₂ -C₄paraffins at ambient temperature or below its ignition temperature,

(b) preheating steam and the mixture of oxygen or air enriched withoxygen and ethane or C₂ -C₄ paraffins to a temperature between about550° C. and about 850° C.

(c) admixing said preheated steam with said preheated mixture of oxygenor air enriched with oxygen and ethane or C₂ -C₄ paraffins,

(d) passing continuously the resulting admixture feed over the saidimproved supported catalyst diluted with the said inert solid (i.e.catalyst diluent) with the volume ratio of catalyst diluent to catalystbetween about 0.05 and about 500 in a fixed bed reactor, maintaining themole ratio of hydrocarbon to oxygen and steam in said admixture feedbetween about 2.5 and about 75 and between about 0.1 and about 10,respectively, a gas hourly space velocity of said admixture feed betweenabout 5×10² cm³.g¹ catalyst.h⁻¹ and about 6×10⁵ cm³ g.⁻¹ catalyst. h⁻¹,a reaction temperature between about 600° C. and about 1000° C. and apressure between about 0.5 atm and about 7.5 atm and cooling andseparating the components of effluent product gases by known methods andrecycling the unconverted reactants.

The preferred other rare earth element, R, is Ce, Nd, Sm, Eu, Gd, Yb, ora mixture thereof. The preferred other alkaline earth element, A, is Mg,Ca or a mixture thereof. The preferred A/Sr mole ratio, a, is in therange of about 0.01 to about 1.0. The preferred loading of A_(a) SrO_(b)on the precoated support, x, is in the range of about 2.5 wt % to about25 wt %. The preferred R/La mole ratio, c, is in the range of about 0.01to about 1.0. The preferred loading of R_(c) LaO_(d) on support, y, isin the range from about 3.0 wt % to about 30 wt %. The preferred anion,Y, in the compounds LaY_(g) and RY_(g), is nitrate anion or acetateanion. The preferred anion, X, in the compounds SrX_(f) and AX_(f), isnitrate anion or acetate anion. The preferred known method used for theprecoating of support with the compounds of lanthanum and other rareearth elements and also for the deposition of the compounds of strontiumand other alkaline earth elements, is the impregnation of solublecompounds from their solution on the surface of catalyst support by theincipient wetness method or the wet impregnation method. The preferredcalcination temperature of the precoated support and the supportedcatalyst is in the range of about 800° C. to about 1000° C. Thepreferred gas atmosphere for the calcination of the precoated supportand the supported catalyst is air.

Because of the use of sintered low surface area inert porous supportmade-up of refractory material in the catalyst preparation, the chemicalinteractions of the catalyst components with the support are eliminatedor greatly reduced and also the supported catalyst has very high thermalstability, mechanical strength and attrition resistance. The surfacearea, porosity and texture of the support are not influenced orinfluenced only to a very small extent during the calcination andoperation of the supported catalyst at high temperatures.

The precoating of the support with the rare earth oxides in step (i) ofthe catalyst preparation is very important. Because of the precoating, alayer of the rare earth oxides exists between the support and thealkaline earth oxides and therefore a direct contact and consequentlythe chemical interactions between the support and the alkaline earthmetal oxides are avoided or greatly reduced. Another important role ofthe precoating is to provide more surface for the dispersion of thealkaline earth metal oxides and also to provide resistance againstsintering to the catalytically active components during the longoperation of the catalyst, when SrO with other alkaline earth oxides isdeposited directly on the support, the resulting catalyst shows everypoor activity, selectivity and productivity in the oxidative coupling ofmethane to higher hydrocarbons.

Because of the incorporation of other alkaline earth and rare earthelements alongwith strontium and lanthanum, respectively, in thecatalyst, a synergetic effect causing an enhancement in the catalyticactivity, selectivity and productivity is produced due to presence ofstrontium and other alkaline earth metal oxides together and/or thepresence of lanthanum and other rare earth oxides together in thecatalyst.

The slow drying of wet mass in both the catalyst preparation steps isimportant because when the wet mess is dried first slowly at about 60°C. and then at higher temperature at about 110° C. the distribution ofthe supported components is uniform throughout the catalyst.

The product obtained from the process of this invention is an improvedsupported catalyst comprising of strontium oxide with other alkalineearth oxides, deposited on a sintered low surface area porous inertsupport precoated with the oxides of lanthanum and other rare earthelements, useful for the oxidative coupling of methane to higherhydrocarbons (i.e. C₂ +-hydrocarbons), oxidative conversion of naturalgas to ethylene and other lower olefins (propylene and butylenes) andalso for the oxidative dehydrogenation of ethane or lower alkanes (C₂-C₄ alkanes) to C₂ -C₄ olefins, in the presence of free oxygen (i.e.gaseous oxygen). The catalyst is generally not reducible and also it isthermally and hydrothermally very stable under the operating conditionsof these processes.

In the oxidative conversion of ethane or C₂ -C₄ alkanes to ethylene andhigher olefins at 700°-900° C., following exothermic and endothermicreactions can occur.

Exothermic Reactions

(a) Oxidative dehydrogenation of ethane or C₂ -C₄ alkanes

    C.sub.2 H.sub.6 +0.5O.sub.2 →C.sub.2 H.sub.4 +H.sub.2 O+25.1 Kcal (1)

Hr=-25.1 Kcal.mol⁻ of C₂ H₆ or

    C.sub.n H.sub.2 n+2+0.5O.sub.2 →C.sub.n H.sub.2 n+H.sub.2 O+heat (2)

(b) Combustion of ethane or C₂ -C₄ paraffins, which is a highlyexothermic reaction

    C.sub.2 H.sub.6 +3.5O.sub.2 →2CO.sub.2 +3H.sub.2 O+341.5 Kcal (3)

Hr=-34.5 Kcal.mol⁻ of ethane

    C.sub.2 H.sub.6 +2.5O.sub.2 →2CO+3H.sub.2 O+206.6 Kcal (4)

Hr=-206.6 Kcal.mol¹ of ethane or

    C.sub.2 -C.sub.4 paraffins+Oxygen→CO, CO.sub.2 and H.sub.2 O+heat (5)

(c) Oxidation of hydrogen to water, which is also highly exothermic

    H.sub.2 +0.5O.sub.2 →H.sub.2 O+59.4 Kcal            (6)

Hr=-59.4 Kcal.mol¹ of H₂

Endothermic reactions: Thermal cracking or non-oxidative pyrolysis ofethane or C₂ -C₄ alkanes

    C.sub.2 H.sub.6 →C.sub.2 H.sub.4 +H.sub.2 -34.18 Kcal (7)

Hr=+34.18 Kcal.mol⁻ of ethane or

    C.sub.2 -C.sub.4 alkanes→C.sub.2 -C.sub.4 oleffins+methane+hydrogen-heat                            (8)

Wherein, Hr=heat of reaction.

When the overall process is highly exothermic, particularly when theselectivity is not very high and also when the catalyst is highly activeand when operated at very high space velocity or very low contact times,which resulted in a production of a large amount of heat in a smallamount of catalyst, there are serious problems for the removal of heatfrom the reactor and also there is a possibility of reaction run-awaycondition if the rate of heat produced surpasses the rate of heatremoval from the reactor. Hence, in order to avoid the possibility ofreaction run-away condition and also to make the process operation verysafe, it is very essential for the process to use catalyst having highselectivity and also to provide large enough heat transfer area requiredfor the removal of heat by the conventional known methods from thereactor. The severity of the process due to the exothermic reactions canbe greatly reduced by allowing the occurrence of the endothermichydrocarbon cracking or pyrolyis to an appreciable extent simultaneouslywith the exothermic hydrocarbon oxidation reactions so that at least apart of the heat produced is used instantly by the endothermicreactions, thus not only reducing the process severity but also makingthe process most energy efficient. This can be achieved by providing alarge contact time, in the vicinity of the catalyst, for the endothermicreactions, which are non-catalytic and hence are slower than thecatalytic hydrocarbon oxidative conversion reactions, so that theendothermic reactions can occur to an appreciable extent. In aconventional catalytic fixed bed reactor, the contact time for theendothermic cracking or pyrolysis reactions is provided by the voidsbetween the catalyst particles, which is very small and hence not enoughfor the endothermic reaction to occur to an appreciable extent. Hence,there is a need to develop a process wherein the contact time providedfor the endothermic reactions relative to that provided for thecatalytic exothermic reactions is large enough so that the endothermicreactions occur to an appreciable extent simultaneously with theexothermic reactions, thus making the process most energy efficient andalso very safe.

The present energy crisis and/or high energy cost, high price of C₂ -C₄paraffins and also the environmental pollution problems have created agreat need for developing a catalytic process for the oxidativeconversion of ethane or C₂ -C₄ alkanes to ethylene and higher olefinswhich requires little or no external energy, operates in a most energyefficient manner and with high conversion, selectivity and productivityand also has absolutely no hazards (i.e. very safe operation). Thisinvention is, therefore, made with the above objects so that most of thedrawbacks or limitations of the earlier processes could be overcome.

In the said process, the preferred reaction temperature is between about700° C. and about 900° C.; the preferred pressure ranges from about 1atm to about 5 atm; the preferred mole ratio of hydrocarbon to oxygenand steam in the feed ranges from about 3 to about 30 and about 0.3 toabout 3, respectively; the preferred gas hourly space velocity of thefeed ranges from about 1×10³ cm³.g⁻¹ catalyst.h⁻¹ to about 3×10⁵ cm³ g⁻¹catalyst.h⁻¹ ; the preferred volume ratio of catalyst diluent tocatalyst ranges from about 0.1 to about 150.

For the improved supported catalyst used in the said process, thepreferred alkaline earth element A is Mg, Ca or a mixture thereof; thepreferred rare earth element R is Ce, Nd, Sm, Eu, Gd, Yb or a mixturethereof; the preferred A/Sr mole ratio, a, ranges from about 0.01 toabout 1.0; the preferred R/La mole ratio, c ranges from about 0.01 toabout 1.0; the preferred loading of alkaline earth oxides, x, rangesfrom about 2.5 wt % to about 25 wt %,; the preferred loading of rareearth oxides, y, ranges from about 3 wt % to about 30 wt %; the support,S, is in the form of granules of size in the range of about 0.1mm toabout 8.0 mm or in the form of spherical or cylindrical pellets,extrudes, rings, saddles or star of diameter or size in the range ofabout 1.0 mm to about 15 mm and has surface area, pore volume andporosity in the range of about 0.001 m².g⁻¹ to about 5.0 m².g⁻¹, about0.02 cm³.g⁻¹ to about 0.6 cm³.g⁻¹ and about 5% to about 75%,respectively.

Said catalyst without support, i.e. containing only mixed rare andalkaline earth oxides can also be employed in the process of thisinvention but the use of improved supported catalyst in this process ispreferred.

The said process can be operated in a fixed bed reactor, such as atubular reactor, a multitubular reactor or a radial flow reactor with anarrangement for removing heat from the reactor operatednon-adiabatically. The process can also be operated adiabatically (i.e.without providing or removing heat from the reactor) when the net heatof reactions in the process is very small. The use of radial flowreactor is preferred particularly when the process is operated at veryhigh space velocity to avoid high pressure drop across the catalyst bed.

In the said process, the products formed are ethylene, higher olefins(mainly propylene and butylenes with much smaller amounts of C₅ +olefins), methane, hydrogen, carbon monoxide, carbon dioxide and water.The gaseous product stream comprises of ethylene, propylene, butylenes,traces of C₅ + olefins, methane, H₂, CO, CO₂, H₂ O and unconvertedethane or C₂ -C₄ paraffins and oxygen or air components.

The feed used in the said process comprises of ethane or C₂ -C₄praffins, oxygen or air enriched with oxygen, and steam. The hydrocarboncomponents of the feed and oxygen are reactants but steam is a feeddiluent and acts as an indirect reactant for the gasification of thecarbon formed in the process under oxygen deficient conditions or bythermal cracking or pyrolysis of hydrocarbons. The presence of steam inthe feed has two beneficial effects: one, the formation of coke andtar-like product in the process are avoided and second, the severity ofthe exothermic hydrocarbon oxidation reactions is reduced due to thefeed dilution. The steam in the product stream can be easily separatedsimply by its condensation. The preheating of the feed gases can beeffected by exhanging heat between the hot reactor effluent product gasstream and the feed gases by the known conventional methods.

The role of catalyst dilution by the inert solid in the process of thisinvention is two fold; one, to provide a larger .heat transfer area ofthe removal of heat from the reactor and thereby making easier theprocess control on the reaction temperature rise due to the heatproduced in the exothermic oxidative hydrocarbon conversion reactions(Reactions 1-6) and second, to provide a large contact time, in a closevicinity of the catalyst, throughout the reactor for the endothermicthermal cracking or pyrolysis reactions (Reactions 7 and 8) as that boththe exothermic and endothermic reactions can occur simultaneously in aclose vicinity of each other and thereby the heat produced in theexothermic reactions is used instantly in the endothermic reactions,thus making the process most energy efficient and its operation verysafe.

Since the thermal hydrocarbon cracking reactions have high activationenergy, their reaction rate increases very fast with the increase in thetemperature. The coupling of the exothermic and endothermic reactions,as described above, leads to an establishment of a sort of bufferingaction for the reaction temperature in the process thus restricting thetemperature rise and, therefore, an occurrence of run-away reactioncondition during the operation of the process is totally eliminated.Because of the coupling of the exothermic and endothermic reactionsoccurring simultaneously, the process of this invention can be mademildly exothermic, near thermoneutral or mildly endothermic bymanipulating the process conditions. The process can be operated in anon-adiabatic fixed bed reactor without any serious problems forremoving heat from the reactor, when the process is mildly exothermic orproviding energy to the reactor, when the process is mildly endothermic,thus requiring no or little external energy, respectively. The processcan also be operated adiabatically with no need to remove heat from thereactor or to provide heat to the reactor, particularly when the processis operated with near zero heat formation or when it is very mildlyexothermic or endothermic. Because of the use of a simple adiabaticreactor for the process, several engineering problems concerning thereactor design, material of construction, process design and control aresimplified and also the capital and operation cost of the process ismuch lower.

By the process of this invention, ethane or C₂ -C₄ paraffins can beconverted to ethylene with high conversion, selectivity and productivityand also in a most energy efficient and safe manner with requirement oflittle or no external energy.

The present invention is described with respect to the followingexamples illustrating the process of this invention for the simultaneousoxidative dehyrogenation and cracking of ethane, which is arepresentative of C₂ =C₄ paraffins to ethylene using the improvedsupported catalyst in a most safe and energy efficient manner. Theseexamples are provided for illustrative purposes only and are not to beconstrued as limitations on the invention.

In the oxidative conversion of methane or natural gas to ethylene,ethane and higher hydrocarbons at 800°-900° C., following exothermic andendothermic reactions occur simultaneously.

Exothermic Reactions

(a) Oxidative coupling of methane

    2CH.sub.4 +0.5O.sub.2 →C.sub.2 H.sub.6 +H.sub.2 O+41.37 Kcal (1)

Hr=-20.68 Kcal.mol⁻¹ of CH₄

(b) Oxidative dehydrogenation of ethane and higher alkanes

    C.sub.2 H.sub.6 +0.5O.sub.2 →C.sub.2 H.sub.4 +H.sub.2 O+25.15 Kcal (2)

Hr=-25.15 Kcal.mol⁻ of C₂ H₆

    C.sub.3 + alkanes+Oxygen→C.sub.3 olefins+water+heat (3)

(c) Combustion of methane and higher hydrocarbons, which is a highlyexothermic process

    CH.sub.4 +20.sub.2 →+2H.sub.2 O+191.5 Kcal          (4)

H_(r) =-191.5 Kcal.mol-1 of CH₄

    CH.sub.4 +3/20.sub.2 →CO+2H.sub.2 O+124.1 Kcal      (5)

H_(r) =-124.1 Kcal. mol⁻¹ of CH₄

    Higher hydrocarbons+Oxygen→CO, CO.sub.2 and H.sub.2 O+heat (6)

Endothermic reactions:: Thermal cracking or non-oxidative pyrolysis ofethane and higher alkanes

    (a) C.sub.2 H.sub.6 →C.sub.2 H.sub.4 +H.sub.2 -34.28 Kcal (7)

H_(r) =+34.28 Kcal.mol⁻¹ of ethane

    (b) C.sub.3 + alkanes→olefins+hydrogen-heat         (8)

Wherein, H_(r) =heat of reaction.

When the overall process is highly exothermic, particularly when theselectivity is below about 70% and also when the catalyst is highlyactive and hence operated at very high space velocity or very lowcontact times, which results in a production of a large amount of heatin a small amount of catalyst, there are serious problems for theremoval of heat from the reactor and also there is a possibility ofreaction run-away condition if the rate of heat produced surpasses therate of heat removal from the reactor. Hence in order to avoid thepossibility of reaction run-away condition and also to make the processoperation very safe, it is very essential for the process to usecatalyst having high selectivity and also to provide large enough heattransfer area required for the removal of heat by the conventional knownmethods from the reactor. The severity of the process due to theexothermic reactions can be greatly reduced by allowing the occurrenceof the endothermic hydrocarbon cracking or pyrolysis to an appreciableextent simultaneously with the exothermic hydrocarbon oxidationreactions so that at least a part of the heat produced is used instantlyby the endothermic reactions, thus not only reducing the processseverity but also making the process most energy efficient. This canhowever be achieved only by providing a large contact time, in thevicinity of the catalyst, for the endothermic reactions, which arenon-catalytic and hence are slower than the catalytic hydrocarbon canoxidative conversion reactions, so that the endothermic reactions canoccur to an appreciable extent. In a conventional catalytic fixed bedreactor, the contact time for the endothermic cracking or pyrolysisreactions is provided by the voids between the catalyst particles whichis very small and being not enough for the endothermic reaction to occurto an appreciable extent. Hence, there is a need to develop a processwherein the contact time provided for the endothermic reactions relativeto that provided for the catalytic exothermic reactions is large enoughso that the endothermic reactions occur to an appreciable extentsimultaneously with the exothermic reactions, thus making the processmost energy efficient and also very safe.

In the process disclosed by Brazdil Jr. et. al., (U.S. Pat. No.4,822,944), the endothermic reactions occur in the voids between thepacked catalyst particles and consequently occur with very low contacttime and hence only to a very small extent or occur in two separatezones in the reactor-zone the catalyst-zone and second, the pyrolysiszone connected in series and therefore the catalytic exo-thermic andnon-catalytic or homogeneous endothermic reactions do not occursimultaneously in close vicinity to each other but in a series and awayfrom each other in the two separate zones, because of this the heatproduced in the exothermic reaction is not used effectively for theendothermic reactions. Also, since the pyrolysis zone is separated fromthe catalyst zone, the operation of the process in the catalysts zone,where the exothermic reactions occur, is not safe because of the reasonsgiven above.

The present energy crisis and/or high energy cost, high methane ornatural gas price and also the environmental pollution problems havecreated a great need for developing a catalytic process for theoxidative conversion of methane or natural gas to ethylene, ethane andhigher hydrocarbons, which requires little or no external energy,operates in a most energy efficient manner and with high selectivity andalso has absolutely no hazards (i.e. very safe operation). Thisinvention is, therefore, made with these objects so that most of thedrawbacks or limitations of the earlier processes could be overcomes.

Definition of Terms Used in the Examples

Total conversion of reactant (%)=mol % of the reactant converted to allproducts.

Conversion of a reactant to a particular product=mol % of the reactantconverted to the particular product.

Selectivity for a particular product (%)=100×(Conversion of reactant tothe product (%)/ Total conversion of reactant (%)!. Productivity for aparticular product (mmol.g⁻¹.h⁻¹)=mmoles of the product formed in theprocess per gram of catalyst per hour. Gas hourly space velocity,GHSC=Volume of gaseous reactant mixture, measured at STP (i.e. at 0° C.and 1 atm), passed over a unit weight of catalyst per hour.

All the ratios of reactants or products are mole ratios. All the loadingof catalyst components, expressed as percent loading are wt %.

C₃ + hydrocarbons are the hydrocarbons containing three or more carbonatoms. C₂ + hydrocarbons are the hydrocarbons containing two or morecarbon atoms.

The net heat of reactions, H_(r), in the overall process is defined asfollows:

Net heat of reactions, H_(r) = H_(f) ! products⁻ H_(f) !reactants,wherein, H_(f) !products and H_(f) !reactants are the heat of formationof products and reactants, respectively. The negative value of the netheat of reactions indicate that the overall process is exothermic andthe positive value of the net heat of reactions indicate that theoverall process is endothermic.

EXAMPLES 1 to 12

In these examples, preparation of an improved supported catalyst withdifferent R/La and A/Sr ratios, where R and A are rare earth andalkaline earth elements other than lanthanum and strontium,respectively, and with different loadings of alkaline earth metal oxideson precoated support and rare earth oxides on different supports, by theprocess of this invention is illustrated.

The catalyst is prepared in two steps by the following generalprocedure.

Step 1: Precoating of support with rare earth oxides

Precursor of lanthanum and other rare earth oxides e.g. compounds oflanthanum and other rare earth elements, which on decomposition areconverted into oxide from, with desired R/La mole ratio, are depositedon catalyst support either by impregnating it with water solubleprecursor compounds from their mixed aqueous solution or by coating thesupport with insoluble precursor compounds from their fine slurry. Theimpregnation of soluble precursor compounds on the support is done bythe incipient wetness impregnation method (IWIM) in which a concentratedsolution of the precursor compound just enough in volume to fill all thepores of the support is added to the support or by the wet impregnationmethod (WIM) in which a concentrated solution of the precursor compoundsin excess of volume required for filling all the pores of the support isadded to the support and the excess of solution is removed. The coatingof insoluble precursor compounds is done by making a slurry of thefinely ground compounds in water and mixing it with the support. Afterthe impregnation or the coating, the wet support is dried in air orunder vacuum first slowly at 60° C. for 5 h and then at 110° C. for 2 h.The dried mass is then decomposed by heating it in air, or in N₂ orunder vacuum at a temperature in the range of 400° C. to 700° C. for aperiod in the range of 0.5 h to 15 h. The decomposed mass is thenfinally calcined in air or in N₂ or under vacuum at a temperature in therange of. 800° C. to 1000° C. for a period in the range of 1 h to 20 h.In case the observed loading of the rare earth oxides on the support isfound to be less than the desired one, the above procedure is repeatedso that the desired loading can be obtained.

Step 2: Deposition of alkaline earth metal oxides on the precoatedsupport

Precursor compounds of strontium and other alkaline earth elements withA/Sr mole ratio are deposited on the precoated support, obtained in thefirst step, by impregnating the precoated support with water solubleprecursor compounds from their mixed aqueous solution or by coating theprecoated support with water insoluble precursor compounds from theirmixed fine slurry, by the methods similar to that described in Step 1.After the impregnation or the coating, the wet supported catalyst massis dried, decomposed and then calcined by the procedures similar to thatdescribed in Step 1, to get the improved catalyst of this invention.

The details of the preparation of improved supported catalyst inExamples 1 to 12, not covered in the above procedure, such as theprecursor compounds of lanthanum and other rare earth elements andstrontium and other alkaline earth elements, method of deposition (e.g.)impregnation or coating) and preparation conditions, are given in Tables1-3. The properties of support used in the preparation of improvedsupported catalyst in Examples 1 to 12 are given in Table 4.

EXAMPLE 13

This example illustrates that the improved supported catalyst of thisinvention, prepared in Examples 1 to 12 by varying the catalystpreparation process parameters, shows high conversion with very highselectivity and productivity in the oxidative coupling of methane tohigher hydrocarbons (C₂ +-hydrocarbons) in the presence of free oxygenat low temperature, below 900° C. and at very high space velocity.

The catalytic reaction over the catalyst is carried out in a continuousflow tubular fixed bed quartz reactor packed with the catalyst bypassing over it a feed comprising of reactants at different reactionconditions. The reactor was kept in an electrically heated tubularfurnace. The reaction temperature was measured by Cromel-Alumelthermocouple located in the catalyst bed. The reactor effluent gaseswere cooled at about 0° C. to condense the water from them, using acoiled condenser immersed in ice-water slurry, and then analysed for theproducts and unconverted reactants by an on-line gas chromatograph.

The performance of the catalysts prepared in Examples 1-12 for theoxidative coupling of methane to higher hydrocarbons is evaluated at thefollowing reaction conditions:

Feed: A mixture of pure methane and oxygen.

CH₄ /O₂ mole ratio in in feed: 8.0 and 16.0

Gas hourly space velocity (GHSV): 1,03,200 cm³.g⁻¹.h⁻¹

pressure: 1.2 atm.

Reaction temperature: 850° C.+5° C.

The results obtained at the two different CH₄ /O₂ mole ratios in feedare presented in Tables 5 and 6.

EXAMPLE -14

This example illustrates that the improved supported catalyst of thisinvention, preparation of which is described in Example-1, shows no signof deactivation when used for oxidative coupling of methane to higherhydrocarbons. The time-on-stream activity and selectivity of thecatalyst in the catalytic reaction is measured in the catalytic reactorand by the procedure described in Example-13, at the following reactionconditions:

Feed composition: 80.0 mol % CH₄, 4.0 mol % O₂ and 16.0 mol % steam.

Gas hourly space velocity (GHSV): 1,03,200 cm³.g PT-PT PT1PT

Pressure: 1.2 atom.

Reaction temperature: 850°+5° C.

The results are presented in table 7.

EXAMPLE -15

This example illustrates that the improved supported catalyst of thisinvention shows high activity and selectivity in the oxidativeconversion of natural gas to ethylene and other lower olefins. Theoxicative conversion of natural gas over the improved supported catalystC 6 prepared in Example - 6 is carried out in the reactor and by theprocedure described in Examples-13, at the following process conditions:

Feed: A mixture of natural gas, oxygen and steam

Natural gas/O₂ mole ratio in feed: Varied from 11.5 to 19

H₂ O/natural gas mole ratio in feed: 0 or 1.0

Gas hourly space velocity (GHSV): 1,30,800-2, 52,800 cm³ g⁻¹ h⁻

Pressure: 1.1 atm.

Reaction temperature: 845°-860° C.

The results obtained at different process conditions are presented inTable -8. The composition of natural gas is as follows:

Natural gas composition (mol %):

CH₄ : 88.9%, C₂ H₆ : 6.3%, C₃ H₈ : 2.3% C₄ H₁₀ : 0.9%, CO₂ : 1.1%, N₂ :0.5%

EXAMPLE -16

This example illustrates that the improved supported catalyst of thisinvention also shows very high activity, selectivity and productivity orefficiency in the oxidative dehyrogenation of ethane, which is arepresentative of lower alkanes (i.e. C₂ -C₄ alkanes). The oxidativedehydrogenation of ethane to ethylene over the improved supportedcatalyst C 1 prepared in Example-1 is carried out in the reactor and bythe procedure described in Example-13, at the following reactionconditions:

Feed : A mixture or ethane, oxygen and steam

C₂ H₆ /O₂ mole ratio in feed: 3.0-8.0

C₂ H₆ /H₂ O mole ration in feed: 0.6-1.3

Gas hourly space velocity (GHSV): 18,900-1,97,400 cm³.g⁻¹.h⁻¹

Pressure: 1.2 atm.

Reaction: 750°-860° C.

The results obtained at different process conditions are presented inTable - 9.

EXAMPLES 17 TO 19

In these examples, a process for the preparation of the improvedsupported catalyst with different R/La and A/Sr ratios, where R and Aare rare earth and alkaline earth elements other than lanthanum andstrontium, respectively and with different loadings of rare earth oxideson a commercial support and of alkaline earth metal oxides on theprecoated supports is disclosed.

The catalyst is prepared in two steps by the following generalprocedure.

Step 1: Precoating of support with rare earth oxides

Precursor of lanthanum and other rare earth oxides e.g. compounds oflanthanum and other rare earth elements, which on decomposition areconverted into oxide form, with desired R/La mole ratio, are depositedon a low surface area sintered porous catalyst carrier SA 5205, obtainedfrom Norton Co., U.S.A., by impregnating it with water soluble procursorcompounds from their mixed aqueous solution. The impregnation of solubleprecursor compounds on the support is done by the incipient wetnessimpregnation method (IWIM) in which a concentrated solution of theprecursor compound Just enough in volume to fill all the poress of thesupport is added to the support. After the impregnation, the wet supportis dried in air first slowly at 60° C. for 5 h and then at 110° C. for 2h. The dried mass is then decomposed by heating it in air at atemperature in the range of 450° C. to 600° C. for a period in the rangeof 2 h to 6 h. The decomposed mass is then finally calcined in air at atemperature in the range of 850° C. to 950° C. for a period in the rangeof 3 h to 10 h.

Step 2: Deposition of alkaline earth metal oxides on the precoatedsupport.

Precursor compounds of strontium and other alkaline earth elements withdesired A/Sr mole ratio are deposited on the precoated support, obtainedin the first step, by impregnating the precoated support with watersoluble precursor compounds from their mixed aqueous solution by themethod similar to that described in Step 1. After the impregnation, thewet supported catalyst mass is dried, decomposed and then calcined bythe procedures similar to that described in Step 1, to get the improvedcatalyst.

The details of the preparation of improved supported catalyst inExamples 17 to 19, not covered in the above procedure, such as theprecursor compounds of lanthanum and other rare earth elements andstrontium and other alkaline earth elements. A/Sr and R/La mole ratiosand preparation conditions, are given in Table 10. The support SA-5205comprises of 86.1% Al₂ O₃, 11.8% SiO₂, 0.6% K₂ O, 0.6% K₂ O, 0.4% CaO,0.4% MgO, 0.4% Na₂ O, 0.2% Fe₂ O₃, and <0.05% ZrO₂ +HfO₂ and has surfacearea of <0.05 m₃.g⁻¹, pore volume of 0.35 cm³.g⁻¹ and porosity of 54%

EXAMPLE -20

This example illustrates the process of this invention for thesimultaneous oxidative dehydrogenation and cracking of ethane, which isa representative of C₂ -C₄ paraffins, to ethylene and higher olefins(propylene and butylenes) in the presence of free oxygen and steam atdifferent process conditions, using the improved supported catalystsprepared in Examples 17 to 19 with the dilution of the catalyst bydifferent inert refractory solids with different catalystdiluent/catalyst ratios.

The process using the catalyst diluted with an inert refractory solid iscarried out in a continuous flow tubular fixed bed quartz reactor packedwith the catalyst distributed uniformly in the inert refractory solid(e.g. quartz or SA 5205) particles or pellets having nearly the samesize and shape as that of the catalyst, by passing over the dilutedcatalyst a feed comprising of ethane, oxygen and steam at differentreaction conditions. The reactor was kept in an electrically heatedtubular furnace. The reaction temperature was measured by Chromel-Alumelthermocouple located in the diluted catalyst bed. The reactor effluentgases were cooled at about 0° C. to condense the water from them, usinga coiled condenser immersed in ice-water slurry, and then analyzed forthe products and unconverted reactants by an on-line gas chromatograph.

The process performance for the simultaneous oxidative dehydrogenationand cracking of ethane to ethylene and over the catalysts, prepared inExamples 17 to 19 diluted to different extents, is evaluated at thefollowing process conditions:

Catalyst diluent: Quartz particles or SA 5205 having same size ofparticles or pellets as that of the catalyst used

Catalyst diluent/catalyst ratio (V/V: varied from 0.1 to 130

Feed: A mixture of pure ethane, oxygen and steam

C₂ H₆ /O₂ mole ratio in feed: varied from 4.5 to 20

C₂ H₆ /H₂ O mole ratio in feed: varied from 0.3 to 3.0

Gas hourly space velocity (GHSV): varied from 690 to 2,08,700 cm³.G⁻¹catalyst.h⁻¹

Pressure: 1.2 atm.

Reaction temperature: 800° or 850° C.

The results obtained for the catalysts prepared in Examples 17 to 19 atthe different process conditions are presented in Table 11a and 11b.

The net heat of reactions in the process is quite small with positive ornegative sign, indicating that the process at the corresponding reactionconditions is mildly endothermic or mildy exothermic, respectively. Thisexample illustrates that the process of this invention occurs in a mostenergy efficient and safe manner and also the process can be made mildlyexothermic, near thermoneutral or mildly endothermic by manipulating theprocess conditions.

EXAMPLES 21 TO 25

In these examples, a process for the preparation of the improvedsupported catalyst with different R/La and A/Sr ratios, where R and Aare rare earth and alkaline earth elements other than lanthanum andstrontium, respectively and with different loadings of rare earth oxideson commercial support and of alkaline earth metal oxides on theprecoated supports is disclosed.

The catalyst is prepared in two steps by the following generalprocedure.

Step 1: Precoating of support with rare earth oxides

Precursor of lanthanum and other rare earth oxides e.g. compounds oflanthanum and other rare earth elements, which on decomposition areconverted into oxide form, with desired R/La mole ratio, are depositedon a low surface are sintered porous catalyst carrier SA 5205, obtainedfrom Norton Co. U.S.A., by impregnating it with water soluble precursorcompounds from their mixed aqueous solution. The impregnation of solubleprecursor compounds on the support is done by the incipient wetnessimpregnation method (IWIM) in which a concentrated solution or theprecursor compound Just enough in volume to fill all the pores of thesupport is added to the support. After the impregnation, the wet supportis dried in air first slowly at 60° C. for 5 h and then at 110° C. for 2h. The dried mass is then decomposed by heating it in air at atemperature in the range of 450° C. to 600 ° C. for a period in the raneof 2 h to 7 h. The decomposed mass is then finally calcined in air at atemperature in the range of 850° C. to 950° C. for a period in the rangeof 3 h to 10 h.

Step 2: Deposition of alkaline earth metal oxides on the precoatedsupport

Precursor compounds of strontium and other alkaline earth elements withdesired A/Sr mole ratio are deposited on the precoated support, obtainedin the first step, by impregnating the precoated support with watersoluble precursor compounds from their mixed aqueous solution by themethod similar to that described in Step 1. After the impregnation, thewet supported catalyst mass is dried, decomposed and then calcined bythe procedures similar to that described in Step 1, to get the improvedcatalyst.

The details of the preparation of improved supported catalyst inExamples 21 to 25, not covered in the above procedure such as theprecursor Compounds of lanthanum and other rare earth elements andstronium and other alkaline earth elements, A/Sr and R/La mole ratio andpreparation conditions, are given in Tables 12. The support SA-5205comprises of 86.1% Al₂ O₃, 11.8% SiO₂, 0.6% K₂ O, 0.4% CaO, 0.4% MgO,0.4% Na₂ O₃, and <0.05% ZrO₂ +HfO₂ and has surface area of <0.05 m³.g⁻¹,pore volume of 0.35 cm³.g⁻¹ and porosity of 54%

EXAMPLE -26

This example illustrates the process of this invention for the oxidative.conversion of methane to ethylene, ethane and higher hydrocarbons (C₃ +hydrocarbons) in the presence of free oxygen at a temperature below 900°C. and at very high space velocity using the improved supported catalystprepared in Examples 21 to 25 with the catalyst dilution by differentinert refractory solids.

The catalytic reaction over the catalyst diluted with an inertrefractory solid is carried out in a continuous flow tubular fixed bedquartz reactor packed with the catalyst distributed uniformly in theinert refractory solid (e.g. quartz or SA 5205) particles or pelletshaving nearly the same size and shape as that of the catalyst, bypassing over the diluted catalyst a feed comprising of reactants atdifferent reaction conditions. The reactor was kept in an electricallyheated tubular furnace. The reaction temperature was measured byChromel-Alumel-thermocouple located in the diluted catalyst bed. Thereactor effluent gases were cooled at about 0° C. to condense the waterfrom them, using a coiled condenser immersed in ice-water slurry, andthe analyzed for the products and unconverted reactants by an on-linegas chromatograph.

The process performance for the oxidative conversion of methane toethylene, ethane and higher hydrocarbons over the catalysts prepared inExamples 21 to 25 is evaluated at the following process conditions:

Catalyst diluent: Quartz particles or SA 5205 having Some size ofparticles or pellets as that of the catalyst used

Catalyst diluent/catalyst ratio (v/v): 1.0

Feed : A mixture of pure methane, oxygen and steam

CH₄ /O₂ mole ratio in feed: varied from 4.0 to 24

H₂ /CH₄ mole ratio in feed: varied from 0.01 to 1.0

Gas hourly space velocity (GHSV): varied from 66,500 to 2,32,760 cm³.g⁻¹catalyst.h⁻¹

Pressure: 1.2 atm

Reaction temperature: varied from 855° C. to 890° C.

The results obtained at the different process conditions are presentedin Table 13.

EXAMPLE -27

This example illustrates the process of this invention for the oxidativeconversion of methane to ethane, and higher hydrocarbons C₃ +hydrocarbons), using the improved supported catalyst C-3 and C-5,prepared in Examples-23 and 25, respectively, with catalyst diluent tocatalyst ratio (v/v) of 27.0 at the different process conditions.

The process was carried out in the reactor and by the procedure similarto that described in Example-26, at the following process conditions:

Catalyst diluent: SA 5205 having particle size same as that of thesupported catalyst

Catalyst diluent/catalyst ratio (v/v): 27.0

Feed : A mixture of pure methane, oxygen and steam

CH₄ /O₂ mole ratio in feed: 15.4 or 21.5

H₂ O/CH₄ mole ratio in feed: 0.3 or 1.1

Gas hourly space velocity (GHSV): 1,16,500 or 1,20,100 cm³.g⁻¹catalyst.h⁻¹

Pressure: 1.2 atm.

Reaction: varied from 850° to 890° C.

The results obtained for the two catalysts at the different processconditions are presented in Table 14.

EXAMPLE-28

This example illustrates the process of this invention for the oxidativeconversion of natural gas to ethylene and higher hydrocarbons using theimproved supported catalyst diluted with the support SA 5205 used in thesupported catalyst. The oxidative conversion of natural gas over theimproved supported catalyst, C-5, prepared in Example-25 and dilutedwith SA 5205 is carried out in the reactor and by the procedure similarto that described in Examples-6, at the following process conditions:

Catalyst diluent: 1 mm size particles of SA 5205

Catalyst diluent/catalyst: 1.0 or 57.0

Feed: A mixture of natural gas, oxygen and steam

Natural gas/O₂ mole ratio in feed: varied from 10 to 20

H₂ O/Natural gas mole ratio in feed: 0.4 or 1.0

Gas hourly space velocity (GHSV): varied from 1,02,710 to 3,59,450cm³.g⁻¹ catalyst.h⁻¹

Pressure: 1.5 atm.

Reaction temperature: varied from 850° to 890° C.

The results obtained at different process conditions are presented inTable -15. The composition of natural gas is as follows:

Natural gas composition (mol %)

CH₄ : 88.9%, C₂ H₆ : 6.3%, C₃ H₈ : 2.3%

C₄ H₁₀ : 0.9%, CO₂ : 1.1%, CO₂ : 0.5%

The net heat of reaction in the exothermic process is quite small andcan be controlled by controlling the process conditions, particularlynatural gas/O₂ ratio in the feed.

Main advantage and/or major improvements achieved by this invention overthe earlier inventions are as follows:

(I) The improved supported catalyst of this invention contains only veryhigh melting components, melting much above 1500° C. and hence thecatalyst is thermally very stable during its operation for a very longperiod and also does not deactivate due loss of any active catalystcomponent during its operation in the high temperature processes.

(II) Because of the use of sintered low surface area porous inertsupport made-up refractory material in the catalyst preparation, thechemical interactions of the catalyst components with the support areeliminated or greatly reduced and also supported catalysts has very highthermal stability, mechanical strength and attrition resistance.

(III) The incorporation of the other alkaline earth and rare earthelements along with strontium and lanthanum, respectively, in thecatalyst results in a synergetic effect causing an enhancement in theactivity, selectivity and productivity of the catalyst due to thepresence of strontium and other alkaline earth metal oxides together andalso due to the presence of lanthanum and other rare earth oxidestogether in the catalyst. Further there exists a layer of rare earthoxides between the support and the alkaline earth metal oxides andthereby direct contact and consequently chemical interactions betweenthe support and the alkaline earth metal oxides are avoided or greatlyreduced. Because of these reasons, the improved supported catalystprepared by the process of this invention, shows very high activity,selectivity and productivity without catalyst deactivation in theoxidative coupling of methane to higher hydrocarbons, in the oxidativeconversion of natural gas to ethylene and other lower olefins and alsoin the oxidative dehydrogenation of lower alkanes to the correspondingolefins, in the presence of free oxygen. Further, the improved supportedcatalyst shows not only higher activity, selectivity and productivity inthe above processes but also operates at lower temperatures, below 900°C.

(I) The improved supported catalyst contains only very high meltingcomponents, melting much about 1500° C., and hence the catalyst isthermally or hydrothermally very stable during its operation for a verylong period and also does not deactivate due to loss of any activecatalyst component during its operation in the high temperatureprocesses.

(II) Because of the use of sintered low surface area porous inertsupport made-up refractory material in the catalyst preparation, thechemical interactions of the catalyst components with the support areeliminated or greatly reduced and also supported catalysts has very highthermal stability, mechanical strength and attrition resistance.

(III) The incorporation of the other alkaline earth and rare earthelements along with strontium and lanthanum, respectively, in thecatalyst results in a synergetic effect causing an enhancement in theactivity, selectivity and productivity of the catalyst due to thepresence of strontium and other alkaline earth metal oxides together andalso due to the presence of lanthanum and other rare earth oxidestogether in the catalyst. Further there exists a layer of rare earthoxides between the support and the alkaline earth metal oxides andthereby direct contact and consequently chemical interactions betweenthe support and the alkaline earth metal oxides are avoided or greatlyreduced. Because of these reasons, the improved supported catalyst showsvery high activity, selectivity and productivity without catalystdeactivation in the oxidative dehydrogenation of ethane or C₂ -C₄paraffins in the presence of free oxygen.

(IV) In the process of this invention, the catalyst is diluted with aninert refractory solid by uniformly distributing the catalyst particlesor pellets in the bed of the catalyst diluent. Because of the catalystdilution, more surface for the heat transfer is available for removingthe exothermic heat of the process, thus eliminating the seriousproblems associated with the removal of heat from the reactor and alsoavoiding the formation of hot spot in the catalyst bed and consequentlyeliminating the risk of reaction run-away conditions. Further thecatalyst dilution also provides more contact time for the homogeneous ornon-catalytic endothermic hydrocarbon cracking reactions occurringsimultaneously with the catalytic exothermic oxidative hydrocarbonconversion reactions in the vicinity of the catalyst.

(V) Further, in the process of this invention, the feed is diluted withsteam. Because of the feed dilution the severity of the exothermicreactions in the process is reduced. Also, because of the presence ofsteam in the feed, there is no coke deposition on the catalyst orreactor walls even under the oxygen deficient conditions and also thereis no formation of tar-like product in the process.

(VI) In the process of this invention, because of the simultaneousoccurrence of the endothermic hydrocarbon cracking reactions to anappreciable extent and the exothermic oxidative hydrocarbon conversionreactions in a close vicinity of each other, the heat produced in theexothermic reactions is used instantly in the endothermic reactions. Thecoupling of the exothermic reactions with the endothermic ones hasimparted following outstanding features to the process of the presentinvention over the earlier processes:

(i) The process is operated in a most energy efficient manner.

(ii) The process is operated in a very safe manner without formation ofhot spots in the reactor and with no possibility of reaction run-awayconditions.

(iii) The process can be made mildly exothermic, near thermoneutral ormildly endothermic by manipulating the process conditions.

(iv) The process can be operated in a non-adiabatic fixed bed reactorwithout any serious problems for removing heat from the reactor, whenthe process is mildly exothermic or providing energy to the reactor,when the process is mildly endothermic, thus requiring no or littleexternal energy, respectively.

(v) The process can also be operated adiabatically with no need toremove heat from the reactor or to provide heat to the reactor,particularly when the process is operated with near zero heat formationor when it is very mildly exothermic. Because of the use of a simpleadiabatic reactor for the process, several engineering problemsconcerning the reactor design, material of construction, process designand control are simplified and also the capital and operation cost ofthe process is much lower.

In the process of this invention, the improved supported catalyst,containing mixed strontium and other alkaline earth oxides deposited ona sintered low surface area porous catalyst support precoated with mixedlanthanum and other rare earth oxides, is employed for the oxidativeconversion of methane or natural gas to ethylene, ethane and higherhydrocarbons. The main advantage of the improved catalyst over theearlier catalysts used for this process are as follows:

(I) The improved supported catalyst contains only very high meltingcomponents, melting much above 1500° C. and hence the catalyst isthermally very stable during its operation for a very long period andalso does not deactivate due to loss of any active catalyst componentduring its operation in the high temperature processes.

(II) Because of the use of sintered low surface area porous inertsupport made-up refractory material in the catalyst preparation, thechemical interactions of the catalyst components with the support areeliminated or greatly reduced and also supported catalysts has very highthermal stability, mechanical strength and attrition resistance.

(III) The incorporation of the other alkaline earth and rare earthelements along with strontium and lanthanum, respectively, in thecatalyst results in a synergetic effect causing an enhancement in theactivity, selectivity and productivity of the catalyst due to thepresence of strontium and other alkaline earth metal oxides together andalso due to the presence of lanthanum and other rare earth oxidestogether in the catalyst. Further, there exists a layer of rare earthoxides between the support and the alkaline earth metal oxides andthereby direct contact and consequently chemical interactions betweenthe support and the alkaline earth metal oxides are avoided or greatlyreduced. Because of these reasons, the improved supported catalyst showsvery high activity, selectivity and productivity without catalystdeactivation in the oxidative conversion of methane or natural gas toethylene, ethane and higher hydrocarbons in the presence of free oxygen.Further, the improved supported catalyst shows not only higher activity,selectivity and productivity in the above process but also operates atlower temperatures (below 900° C.). Furthermore, the catalyst also showshigh activity, selectivity and productivity in oxidative dehydrogenationof ethane to ethylene at the operating conditions of the above process.

(IV) In the process of this invention, the catalyst is diluted with aninert refractory solid by uniformly distributing the catalyst particlesor pellets in the bed of the catalyst diluent. Because of the catalystdilution, more surface for the heat transfer is available for removingthe exothermic heat of the process, thus eliminating the seriousproblems associated with the removal of heat from the reactor and alsoavoiding the formation of hot spot in the catalyst bed and consequentlyeliminating the risk of reaction run-away conditions. Further thecatalyst dilution also provides more contact time for the homogeneous ornon-catalytic reactions occurring simultaneously with the catalyticreactions, in the vicinity of the catalyst.

(V) The process of this invention is highly energy efficient because ofthe simultaneous occurrence of the endothermic reactions, hydrocarboncracking to an appreciable extent due to the provision of higher contacttime in the vicinity of the catalyst due to its dilution with an inertsolid, with the exothermic oxidative hydrocarbon conversion reactions;the heat produced in the exothermic reactions is used-up, at leastpartly, in the endothermic reactions. Because of this the net heatproduced is small enough to be removed from the reactor easily withoutany serious problems and hence there is no risk of reaction run-awayconditions, thus making the process operation much more safer and alsomost energy efficient.

(IV) Furthermore, in the process of this invention, the feed is dilutedwith steam. Because of the feed dilution the severity of the exothermicreactions in the process is reduced. Also, because of the presence ofsteam in the feed, there is no coke deposition on the catalyst orreactor walls even under the oxygen deficient conditions and also thereis no formation of tar-like product in the process.

(VII) Finally, the process of this invention is much safer because ofthe above and also because of the lower concentration of oxygen,relative to that of methane or natural gas, used in the feed, which isfar away from the explosion limit.

Details of the production of catalysts described in Examples 1-12 areshown in the following Tables 1-3. Table 4 gives details of theproperties of certain catalysts. Tables 5-9 give details of the use ofcertain catalysts. Table 10 gives details of the preparations of thecatalysts of Examples 17-19 and Tables 11a and 11b refer to the use ofsuch catalysts. Table 12 gives details of the preparation of thecatalysts of Examples 21-25 and Tables 13-15 give details of the use ofsome of these catalysts.

                                      TABLE 1                                     __________________________________________________________________________    Details of the preparation of improved supported catalyst in Example 1 to                   Example 1                                                                            Example 2                                                                            Example 3                                                                            Example 4                                  __________________________________________________________________________    Support used  SA 5205                                                                              SA 5205                                                                              SA 5205                                                                              SA 5205                                    Shape and size of support                                                                   6 mm spheres                                                                         6 mm spheres                                                                         6 mm spheres                                                                         1 mm grannules                             Precoating of the support with rare earth oxides                              Precursor compound of La                                                                    La-nitrate                                                                           La-nitrate                                                                           La-nitrate                                                                           La-nitrate                                 Precursor compound of R                                                                     Nd-nitrate                                                                           Gd-nitrate                                                                           Sm-nitrate                                                                           Nd-nitrate                                 R/La mole ratio                                                                             1.0    1.0    1.0    1.0                                        Method of deposition                                                                        IWIM   IWIM   IWIM   IWIM                                       Decomposition temp. (°C.)                                                            500° C.                                                                       550° C.                                                                       500° C.                                                                       500° C.                             Decomposition atmosphere                                                                    Air    Air    Air    Air                                        Decomposition period (h)                                                                    4 h    3 h    4 h    4 h                                        Calcination temp. (°C.)                                                              950° C.                                                                       900° C.                                                                       950° C.                                                                       900° C.                             Calcination atmosphere                                                                      Air    Air    Air    Air                                        Calcination period (h)                                                                      4 h    6 h    4 h    4 h                                        Loading of rare earth                                                                       16.9%  15.9%  16.1%  10.9%                                      oxides, y (wt %)                                                              Deposition of alkaline earth metal oxides on precoated support                Precursor compound of Sr                                                                    Sr-nitrate                                                                           Sr-nitrate                                                                           Sr-nitrate                                                                           Sr-nitrate                                 Precursor compound of A                                                                     Mg-nitrate                                                                           Ca-nitrate                                                                           Ca-nitrate                                                                           Mg-nitrate                                 A/Sr mole ratio                                                                             1.0    0.1    1.0    1.0                                        Method of deposition                                                                        IWIM   IWIM   IWIM   IWIM                                       Decomposition temp. (°C.)                                                            450° C.                                                                       490° C.                                                                       490° C.                                                                       500° C.                             Decomposition atmosphere                                                                    Air    Air    Air    Air                                        Decomposition period (h)                                                                    4 h    4 h    4 h    3 h                                        Calcination temp. (°C.)                                                              900° C.                                                                       900° C.                                                                       850° C.                                                                       900° C.                             Calcination atmosphere                                                                      Air    Air    Air    Air                                        Calcination period (h)                                                                      4 h    4 h    6 h    4 h                                        Loading of alkaline earth                                                                   10.0%  11.4%  11.1%  10.1%                                      oxides, x (wt %)                                                              Improved supported catalyst                                                                 C 1    C 2    C 3    C 4                                        produced                                                                      __________________________________________________________________________     IWIM = incipient wetness impregnation method                                  C 1 = MgSrO.sub.2 (10.1%)/NdLaO.sub.3 (16.9%)/SA 5205;                        C 2 = Ca.sub.0.1 Sr.sub.1.1 (11.4%)/GdLaO.sub.3 (15.9%)/SA 5205;              C 3 = CaSrO.sub.2 (11.1%)/SmLaO.sub.3 (16.1%)/SA 5205;                        C 4 = MgSrO.sub.2 (10.1%)/NdLaO.sub.3 (10.9%)/SA 5205;                   

                                      TABLE 2                                     __________________________________________________________________________    Details of the preparation of improved supported catalyst in Example 5 to                   Example 5                                                                            Example 6                                                                            Example 7                                                                            Example 8                                  __________________________________________________________________________    Support used  SA 5205                                                                              SA 5218                                                                              SA 5218                                                                              SA 5232                                    Shape and size of support                                                                   3 mm granules                                                                        2 mm granules                                                                        4.5 mm spheres                                                                       4.5 mm spheres                             Precoating of the support with rare earth oxides                              Precursor compound of La                                                                    La-nitrate                                                                           La-nitrate                                                                           La-nitrate                                                                           La-nitrate                                 Precursor compound of R                                                                     Ce-nitrate                                                                           Nd-nitrate                                                                           Nd-nitrate                                                                           Eu-nitrate                                 R/La mole ratio                                                                             1.0    0.6    0.2    0.84                                       Method of deposition                                                                        IWIM   IWIM   IWIM   IWIM                                       Decomposition temp. (°C.)                                                            510° C.                                                                       500° C.                                                                       400° C.                                                                       480° C.                             Decomposition atmosphere                                                                    Air    Air    Air    Air                                        Decomposition period (h)                                                                    4 h    4 h    6 h    28 h                                       Calcination temp. (°C.)                                                              900° C.                                                                       930° C.                                                                       950° C.                                                                       800° C.                             Calcination atmosphere                                                                      Air    Air    Air    Air                                        Calcination period (h)                                                                      6 h    4 h    3 h    10 h                                       Loading of rare earth                                                                       17.8%  16.1%  17.5%  20.3%                                      oxides, y (wt %)                                                              Deposition of alkaline earth metal oxides on precoated support                Precursor compound of Sr                                                                    Sr-nitrate                                                                           Sr-nitrate                                                                           Sr-nitrate                                                                           Sr-nitrate                                 Precursor compound of A                                                                     Mg-nitrate                                                                           Mg-nitrate                                                                           Ca-nitrate                                                                           Ba-nitrate                                 A/Sr mole ratio                                                                             0.1    1.0    0.2    0.2                                        Method of deposition                                                                        IWIM   IWIM   IWIM   IWIM                                       Decomposition temp. (°C.)                                                            450° C.                                                                       500° C.                                                                       500° C.                                                                       500° C.                             Decomposition atmosphere                                                                    Air    Air    Air    Air                                        Decomposition period (h)                                                                    6 h    4 h    4 h    5 h                                        Calcination temp. (°C.)                                                              950° C.                                                                       1000° C.                                                                      900° C.                                                                       850° C.                             Calcination atmosphere                                                                      Air    Air    Air    Air                                        Calcination period (h)                                                                      3 h    2 h    4 h    5 h                                        Loading of alkaline earth                                                                   12.8%  9.0%   4.1%   17.7%                                      oxides, x (wt %)                                                              Improved supported catalyst                                                                 C 5    C 6    C 7    C 8                                        produced                                                                      __________________________________________________________________________     IWIM = incipient wetness impregnation method                                  C 5 = Mg.sub.0.2 SrO.sub.1.2 (12.8%)/CeLaO.sub.3.5 (17.8%)/SA 5205;           C 6 = MgSrO.sub.2 (9.0%)/Nd.sub.0.6 LaO.sub.2.4 (16.1%)/SA 5218;              C 7 = Ca.sub.0.2 SrO.sub.1.2 (4.1%)/Nd.sub.0.2 LaO.sub.1.8 (17.5%)/SA         5218;                                                                         C 8 = Ba.sub.0.2 SrO.sub.1.2 (17.7%)/Eu.sub.0.04 LaO.sub.1.56 (20.3%)/SA      5205;                                                                    

                                      TABLE 3                                     __________________________________________________________________________    Details of the preparation of improved supported catalyst in Example          9-12                                                                                        Example 9                                                                            Example 10                                                                           Example 11                                                                           Example 12                                 __________________________________________________________________________    Support used  SS 5231                                                                              SA 5552                                                                              SA 5285                                                                              SA 5285                                    Shape and size of support                                                                   4.5 mm spheres                                                                       Rings of 8 aa                                                                        6 mm spheres                                                                         6 mm spheres                                                    OD, 4 mm ID,                                                                  and 7 mm                                                                      length                                                   Precoating of the support with rare earth oxides                              Precursor compound of La                                                                    La-nitrate                                                                           La-nitrate                                                                           La-acetate                                                                           La.sub.2 O.sub.3                           Precursor compound of R                                                                     Nd-nitrate                                                                           Yb-nitrate                                                                           Ce-acetate                                                                           Sa-carbonate                               R/La mole ratio                                                                             0.1    0.2    0.02   0.1                                        Method of deposition                                                                        WIM    WIM    WIM    Coating                                    Decomposition temp. (°C.)                                                            550° C.                                                                       500° C.                                                                       500° C.                                                                       700° C.                             Decomposition atmosphere                                                                    N.sub.2                                                                              Air    Air    vacuum (1 torr)                            Decomposition period (h)                                                                    4 h    6 h    15 h   0.5 h                                      Calcination temp. (°C.)                                                              900° C.                                                                       900° C.                                                                       900° C.                                                                       950° C.                             Calcination atmosphere                                                                      Air    Air    Air    N.sub.2                                    Calcination period (h)                                                                      5 h    4 h    4 h    1 h                                        Loading of rare earth                                                                       21.1%  22.4%  19.9%  27.5%                                      oxides, y (wt %)                                                              Deposition of alkaline earth metal oxides on precoated support                Precursor compound of Sr                                                                    Sr-nitrate                                                                           Sr-nitrate                                                                           Sr-acetate                                                                           Sr-hydroxide                               Precursor compound of A                                                                     Ca-nitrate                                                                           Ba-nitrate                                                                           Mg-acetate                                                                           Ca-hydroxide                               A/Sr mole ratio                                                                             0.2    0.01   0.1    0.1                                        Method of deposition                                                                        WIM    WIM    WIM    Coating                                    Decomposition temp. (°C.)                                                            550° C.                                                                       500° C.                                                                       500° C.                                                                       550° C.                             Decomposition atmosphere                                                                    N.sub.2                                                                              Air    Air    vacuum (1 torr)                            Decomposition period (h)                                                                    4 h    4 h    15 h   6 h                                        Calcination temp. (°C.)                                                              900° C.                                                                       925° C.                                                                       900° C.                                                                       900° C.                             Calcination atmosphere                                                                      Air    Air    Air    N.sub.2                                    Calcination period (h)                                                                      5 h    4 h    4 h    4 h                                        Loading of alkaline earth                                                                   19.2%  20.8%  10.4%  18.7%                                      oxides, x (wt %)                                                              Improved supported catalyst                                                                 C 9    C 10   C 11   C 12                                       produced                                                                      __________________________________________________________________________     WIM = Wet impregnation method                                                 C 9 = Ca.sub.0.2 SrO.sub.1.2 (19.2%)/Nd.sub.0.1 LaO.sub.1.65 (21.1%)/SS       5231;                                                                         C 10 = Ba.sub.0.01 SrO.sub.1.01 (20.8%)/Yb.sub.0.2 LaO.sub.1.8 (22.4%)/SA     5552;                                                                         C 11 = Mg.sub.0.1 SrO.sub.1.1 (10.4%)/Ce.sub.0.02 LaO.sub.1.54 (19.9%)/SA     5205;                                                                         C 12 = Ca.sub.0.1 SrO.sub.1.1 (18.7%)/Sm.sub.0.1 LaO.sub.1.65 (27.5%)/SA      5205;                                                                    

                                      TABLE 4                                     __________________________________________________________________________    Properties of the different sintered low surface area porous supports         used in the preparation of improved supported catalysts in Example            1-12; these supports are obtained from Norton Co., USA.                                                      Surface                                                                            Pore                                                                     area volume                                                                             Porosity                             Support                                                                            Shape                                                                              Composition          (a.sup.2.gm.sup.-1)                                                                (ca.sup.3.q.sup.-2)                                                                (%)                                  __________________________________________________________________________    SA 5285                                                                            spherical                                                                          Al.sub.2 O.sub.3 (86.1%), SiO.sub.2 (11.8%), K.sub.2 O(8.6%)                                       <0.05                                                                              0.35 54                                             CaO(0.4%), MgO(0.4%), Ha.sub.2 O(0.4%),                                       Fe.sub.2 O.sub.3 (0.2%), IrO.sub.2 + HiO.sub.2 (<0.05%)             SA 5218                                                                            spherical                                                                          Al.sub.2 O.sub.3 (86.1%), SiO.sub.2 (12.8%), CaO(0.6%)                                             <0.05                                                                              0.25 48                                             MgO(0.4%), K.sub.2 O(0.4%), TiO.sub.2 (0.2%)                                  Na.sub.2 O(0.2%), Fe.sub.2 O.sub.3 (0.1%), ZrO.sub.2 (<0.05%)       SA 5552                                                                            rings                                                                              Al.sub.2 O.sub.3 (93.1%), SiO.sub.2 (5.6%), Fe.sub.2 O.sub.3                  (0.3%)               <1.00                                                                              0.39 59                                             MgO(0.3%), TiO.sub.2 (0.1%), CaO(0.1%),                                       Na.sub.2 O(0.1%), K.sub.2 O(0.1%), HiO.sub.2 + ZrO.sub.2                      (<0.05%)                                                            SC 5232                                                                            spherical                                                                          SiC(65.8%), SiO.sub.2 (28.5%), Al.sub.2 O.sub.3 (4.7%),                                            <0.3 0.26 43                                             Fe.sub.2 O.sub.3 (0.3%), CaO(0.2%), MgO(0.1%),                                Na.sub.2 O(0.1%), K.sub.2 O(0.1%), ZrO.sub.2 + HiO.sub.2                      (<0.05%),                                                                     TiO.sub.2 (<0.01%), leachable iron = 17 paa                         SS 5231                                                                            spherical                                                                          SiO.sub.2 (95.8%), Al.sub.2 O.sub.3 (4.1%), Fe.sub.2 O.sub.3                  (0.3%),              <0.4 0.25 35                                             TiO.sub.2 (0.2%), CaO(0.1%), MgO(0.1%),                                       Na.sub.2 O(0.1%), K.sub.2 O(0.1%), ZrO.sub.2 + HiO.sub.2                      (<0.05%)                                                            __________________________________________________________________________

                                      TABLE 5                                     __________________________________________________________________________    Results of the oxidative coupling of methane to higher hydrocarbons           over the improved supported catalyst prepared in Examples 1-6.                                 Selectivity                                                         CH.sub.4 /O.sub.2                                                                  CH.sub.4                                                                           (%) for higher                                                                       C.sub.2 H.sub.4 /C.sub.2 H.sub.6                                                     Productivity                                          ratio in                                                                           conversion                                                                         hydrocarbons                                                                         ratio in                                                                             C.sub.2 -hydrocarbon                           Catalyst                                                                             feed (%)  C.sub.2                                                                           C.sub.2+                                                                         products                                                                             (mmol g.sup.-1 h.sup.-1                        __________________________________________________________________________    C 1 (prepared                                                                        8.0  20.5 73.5                                                                              78.6                                                                             0.8    309                                            in Example-1)                                                                        16.0 12.9 82.3                                                                              86.8                                                                             0.6    230                                                   20.0 11.0 84.8                                                                              90.4                                                                             0.5    204                                            C 2 (prepared                                                                        8.0  16.9 75.4                                                                              78.5                                                                             0.8    261                                            in Example-2)                                                                        16.0 10.6 82.6                                                                              87.1                                                                             0.5    190                                            C 3 (prepared                                                                        8.0  18.7 73.6                                                                              78.7                                                                             0.8    282                                            in Example-3)                                                                        16.0 12.3 82.9                                                                              89.6                                                                             0.6    221                                            C 4 (prepared                                                                        8.0  20.7 73.9                                                                              79.1                                                                             0.8    314                                            in Example-4)                                                                        16.0 13.1 81.4                                                                              86.7                                                                             0.6    231                                            C 5 (prepared                                                                        8.0  18.5 74.6                                                                              80.0                                                                             0.8    283                                            in Example-5)                                                                        16.0 11.3 83.1                                                                              87.8                                                                             0.5    203                                            C 6 (prepared                                                                        8.0  20.3 73.1                                                                              79.3                                                                             0.8    304                                            in Example-6)                                                                        16.0 11.9 82.4                                                                              87.5                                                                             0.6    212                                                   20.0 10.5 84.7                                                                              90.7                                                                             0.5    195                                            __________________________________________________________________________

                                      TABLE 6                                     __________________________________________________________________________    Results of the oxidative coupling of methane to higher hydrocarbons           over the improved supported catalyst prepared in Examples 7-12.                                Selectivity                                                         CH.sub.4 /O.sub.2                                                                  CH.sub.4                                                                           (%) for higher                                                                       C.sub.2 H.sub.4 /C.sub.2 H.sub.6                                                     Productivity                                          ratio in                                                                           conversion                                                                         hydrocarbons                                                                         ratio in                                                                             C.sub.2 -hydrocarbon                           Catalyst                                                                             feed (%)  C.sub.2                                                                           C.sub.2+                                                                         products                                                                             (mmol g.sup.-1 h.sup.-1                        __________________________________________________________________________    C 7 (prepared                                                                        8.0  18.7 74.3                                                                              81.1                                                                             0.8    285                                            in Example-7)                                                                        16.0 10.3 83.2                                                                              90.2                                                                             0.5    186                                            C 8 (prepared                                                                        8.0  18.0 68.0                                                                              73.5                                                                             0.9    251                                            in Example-8)                                                                        16.0 10.6 73.5                                                                              78.4                                                                             0.6    169                                            C 9 (prepared                                                                        8.0  18.3 71.2                                                                              77.3                                                                             0.8    267                                            in Example-9)                                                                        16.0 11.5 78.4                                                                              82.5                                                                             0.6    195                                            C 10 (prepared                                                                       8.0  19.2 69.1                                                                              75.7                                                                             0.8    272                                            in Example-10)                                                                       16.0 10.4 79.3                                                                              84.3                                                                             0.7    179                                            C 11 (prepared                                                                       8.0  19.7 72.5                                                                              78.1                                                                             0.8    293                                            in Example-11)                                                                       16.0 12.1 80.3                                                                              84.4                                                                             0.6    210                                            C 12 (prepared                                                                       8.0  17.6 71.3                                                                              75.3                                                                             0.9    256                                            in Example-12)                                                                       16.0  9.5 75.7                                                                              82.5                                                                             0.5    156                                            __________________________________________________________________________

                  TABLE 7                                                         ______________________________________                                        Results showing the time-on-stream activity and                               selectivity of the improved supported catalyst,                               C-1, prepared in Example-1 for the oxidative                                  coupling of methane to higher hydrocarbons.                                                        Selectivity                                                          CH.sub.4 (%) for higher                                                                            C.sub.2 H.sub.4 /C.sub.2 H.sub.6             Time-on-stream                                                                            conversion                                                                             hydrocarbons                                                                              ratio in                                     (h)         (%)      C.sub.2  C.sub.2+                                                                           products                                   ______________________________________                                         1          10.9     84.3     90.1 0.51                                        16         10.6     84.6     90.3 0.50                                        48         11.0     83.1     89.3 0.52                                       101         10.8     83.3     90.0 0.51                                       152         11.2     83.0     89.0 0.53                                       207         10.9     83.7     90.1 0.52                                       314         10.7     84.7     91.3 0.50                                       416         11.0     83.2     89.9 0.52                                       512         10.8     84.6     90.7 0.51                                       ______________________________________                                    

                                      TABLE 8                                     __________________________________________________________________________    Results on the oxidative conversion of natural gas to                         ethylene and lower olefins over the improved supported                        catalyst, C 6, prepared in Example-6                                          Reaction       GHSV of feed                                                                         Conversion of                                           temp.                                                                              Feed ratios                                                                             gases  carbon in NG                                                                         Selectivity (%)                                  (°C.)                                                                       NG/O.sub.2                                                                         H.sub.2 O/NG                                                                       (cm.sup.3.g.sup.-1.h.sup.-1)                                                         to ethylene (%)                                                                      C.sub.2 H.sub.4                                                                   C.sub.2+ -olefins                            __________________________________________________________________________    850  19.0 0.0  1,30,300                                                                             21.1   75.2                                                                              83.4                                         850  13.1 0.0  2,52,800                                                                             16.3   67.3                                                                              84.2                                         860  15.3 0.0  2,52,800                                                                             15.8   68.9                                                                              84.7                                         845  18.4 0.0  2,52,800                                                                             15.1   69.2                                                                              86.1                                         850  15.3 1.0  1,52,700                                                                             19.7   74.7                                                                              85.8                                         __________________________________________________________________________

                                      TABLE 9                                     __________________________________________________________________________    Results on the oxidative dehydrogenation of ethane over the                   improved supported catalyst, C 1, prepared in Example-1                       Reaction       GHSV of feed                                                                         Ethane           Productivity                           temp.                                                                              Feed ratios                                                                             gases  conversion                                                                         Selectivity (%)                                                                           of ethylene                            (°C.)                                                                       C.sub.2 H.sub.6 /O.sub.2                                                           C.sub.2 H.sub.6 /H.sub.2 O                                                         (cm.sup.3.g.sup.-1.h.sup.-1)                                                         (%)  C.sub.2 H.sub.4                                                                  C.sub.2+ -olefins                                                                   CO.sub.x                                                                         (mmol g.sup.-1)                        __________________________________________________________________________    750  3.0  0.6  18,900 60.1 74.1                                                                             77.5  16.1                                                                             124                                    850  3.0  0.6  18,900 89.2 70.3                                                                             74.1  15.7                                                                             175                                    800  4.0  0.7  18,900 70.3 73.5                                                                             78.6  12.1                                                                             157                                    850  4.0  0.7  18,900 80.1 75.1                                                                             80.2  11.3                                                                             183                                    850  8.0  0.7  18,900 77.2 82.3                                                                             87.6  6.1                                                                              209                                    800  8.0  0.7  18,900 58.3 83.4                                                                             88.1  7.2                                                                              160                                    850  8.0  0.6  61,400 73.5 81.2                                                                             86.7  5.9                                                                              589                                    800  8.0  0.6  61,400 51.3 85.5                                                                             88.2  6.1                                                                              433                                    850  8.0  1.0  1,02,000                                                                             65.2 84.9                                                                             88.4  6.2                                                                              1159                                   850  8.0  0.8  1,50,990                                                                             58.9 83.7                                                                             87.5  7.0                                                                              1362                                   860  8.0  1.3  1,97,400                                                                             51.5 84.1                                                                             87.6  6.5                                                                              1985                                   850  6.0  0.8  1,60,400                                                                             64.6 81.2                                                                             83.9  9.3                                                                              1575                                   __________________________________________________________________________

                                      TABLE 10                                    __________________________________________________________________________    Details of the preparation of improved supported catalyst in Example 17       to 19                                                                                       Example 17                                                                            Example 18                                                                             Example 19                                     __________________________________________________________________________    Support used  SA 5205 SA 5205  SA 5205                                        Shape and size of support                                                                   1 mm granules                                                                         2 mm granules                                                                          6 mm spheres                                   Precoating of the support with rare earth oxides                              Precursor compound of La                                                                    La-nitrate                                                                            La-nitrate                                                                             La-nitrate                                     Precursor compound of R                                                                     Nd-nitrate                                                                            Nd-nitrate                                                                             Sm-nitrate                                     R/La mole ratio                                                                             1.0     0.1      0.1                                            Decomposition temp. (°C.)                                                            500° C.                                                                        500° C.                                                                         600° C.                                 Decomposition atmosphere                                                                    Air     Air      Air                                            Decomposition period (h)                                                                    4 h     4 h      4 h                                            Calcination temp. (°C.)                                                              900° C.                                                                        930° C.                                                                         850° C.                                 Calcination atmosphere                                                                      Air     Air      Air                                            Calcination period (h)                                                                      6 h     4 h      10 h                                           y (wt %)      18.6%   18.0%    14.7%                                          Deposition of alkaline earth metal oxides on precoated support                Precursor compound of Sr                                                                    Sr-nitrate                                                                            Sr-nitrate                                                                             Sr-nitrate                                     Precursor compound of A                                                                     Mg-nitrate                                                                            Mg-nitrate                                                                             Ca-nitrate                                     A/Sr mole ratio                                                                             1.0     0.1      0.1                                            Decomposition temp. (°C.)                                                            600° C.                                                                        500° C.                                                                         450° C.                                 Decomposition atmosphere                                                                    Air     Air      Air                                            Decomposition period (h)                                                                    2 h     5 h      6 h                                            Calcination temp. (°C.)                                                              900° C.                                                                        930° C.                                                                         950° C.                                 Calcination atmosphere                                                                      Air     Air      Air                                            Calcination period (h)                                                                      6 h     4 h      3 h                                            Loading of alkaline earth                                                                   12.4%   26.4%    14.1%                                          oxides, x (wt %)                                                              Improved supported catalyst                                                                 C 1     C 2      C 3                                            produced                                                                      __________________________________________________________________________     C 1 = MgSrO.sub.2 (12.4%)/NdLaO.sub.3 (18.6%)/SA 5205;                        C 2 = Mg.sub.0.1 SrO.sub.1.1 (26.4%)/Nd.sub.0.1 LaO.sub.1.65 (18.0%)/SA       5205;                                                                         C 3 = Ca.sub.0.1 SrO.sub.1.1 (14.1%)/Sm.sub.0.1 LaO.sub.1.65 (14.7%)/SA       5205;                                                                    

                                      TABLE 11a                                   __________________________________________________________________________    Results on the oxidative conversion of ethane to                              ethylene and higher hydrocarbons over the improved                            catalyst C-1 prepared in Example 17, with different                           catalyst diluent/catalyst (vol/vol) ratios at different                       process conditions:                                                                                                                     Bet beat                                                                  product-                                                                          of                                                                        ivity                                                                             reac-                                                                     of  tion,               Catalyst                                              ethylene                                                                          H,                  diluent/               GHSV of                        (mol.                                                                             (Kcal.              catalyst                                                                              Reaction                                                                           Feed ratios                                                                             feed gases                                                                          C.sub.2 H.sub.6                                                                    Selectivity (%) for g.sup.-1                                                                          mol.sup.-1 of       Catalyst                                                                          ratio                                                                             temp.                                                                              (mol/mol) (cm.sup.3.g.sup.-1.                                                                 conversion                                                                            C.sub.3+4                                                                         C.sub.3+4    catalyst.                                                                         C.sub.2                                                                       H.sub.6             diluent                                                                           (v/v)                                                                             (°C.)                                                                       C.sub.2 H.sub.6 /O.sub.2                                                           C.sub.2 H.sub.6 /H.sub.2 O                                                         catalyst. h.sup.-1)                                                                 (%)  C.sub.2 H.sub.4                                                                  olefins                                                                           alkanes                                                                           CH.sub.4                                                                         CO CO.sub.2                                                                         h.sup.-1)                                                                         converted           __________________________________________________________________________    Quartz                                                                             8.1                                                                              850  7.94 1.00 1,07,45                                                                             47.5 86.7                                                                             3.16                                                                              1.18                                                                              4.17                                                                             2.46                                                                             2.29                                                                             962 +6.37                       800  7.94 1.00 1407  35.8 86.1                                                                             2.35                                                                              1.61                                                                              4.21                                                                             1.09                                                                             4.61                                                                             9.18                                                                              -7.91                       850  7.94 1.00 1407  68.7 83.3                                                                             3.21                                                                              0.16                                                                              7.35                                                                             2.39                                                                             3.61                                                                             14.93                                                                             +8.50                       800  7.80 0.95 692   48.7 81.2                                                                             2.84                                                                              0.60                                                                              6.23                                                                             4.13                                                                             4.97                                                                             5.62                                                                              -7.95               SA   2.4                                                                              850  7.94 1.00 5217  76.2 83.2                                                                             3.88                                                                              0.14                                                                              7.60                                                                             1.88                                                                             3.87                                                                             69.48                                                                             +13.45              5205    800  7.94 1.00 5217  44.8 85.8                                                                             2.37                                                                              1.72                                                                              4.33                                                                             1.72                                                                             4.84                                                                             42.84                                                                             +1.88               SA  12.2                                                                              850  7.94 1.00 28,870                                                                              69.3 85.9                                                                             3.88                                                                              0.23                                                                              5.86                                                                             2.82                                                                             2.89                                                                             261 +12.37              5205    850  7.75 1.93 18.160                                                                              85.2 79.1                                                                             4.15                                                                              0.09                                                                              11.18                                                                            2.89                                                                             2.62                                                                             199 +18.77                      850  4.50 1.83 28,543                                                                              77.9 78.9                                                                             3.42                                                                              0.28                                                                              7.29                                                                             3.98                                                                             6.21                                                                             285 +7.49                       850  11.94                                                                              1.02 29,655                                                                              78.8 86.8                                                                             4.02                                                                              0.24                                                                              6.39                                                                             0.98                                                                             1.61                                                                             272 +11.37              SA  42.5                                                                              850  7.94 1.00 69,565                                                                              81.5 82.7                                                                             4.84                                                                              0.29                                                                              7.96                                                                             2.29                                                                             1.91                                                                             984 +12.73              5205    850  7.82 0.32 67,965                                                                              84.6 84.3                                                                             3.75                                                                              0.06                                                                              7.81                                                                             1.64                                                                             3.33                                                                             491 +15.29                      850  20.00                                                                              1.06 63,190                                                                              77.2 86.9                                                                             5.21                                                                              0.27                                                                              6.00                                                                             0.54                                                                             1.11                                                                             1836                                                                              +24.41              SA  130.0                                                                             850  7.94 1.00 2,06,700                                                                            76.5 84.7                                                                             4.85                                                                              0.22                                                                              6.19                                                                             2.85                                                                             1.15                                                                             2837                                                                              +14.64              5205    850  7.95 2.89 2,06,700                                                                            76.2 83.9                                                                             5.17                                                                              0.29                                                                              7.87                                                                             2.73                                                                             0.97                                                                             4058                                                                              +12.21              __________________________________________________________________________

                                      TABLE 11b                                   __________________________________________________________________________    Results on the oxidative conversion of ethane to                              ethylene and higher hydrocarbons over the improved                            catalyst C-2 prepared in Example 18 and 19, respectively,                     with different catalyst diluent/catalyst                                      (vol/vol) ratios at different process conditions:                                                                                       Bet beat                                                                  product-                                                                          of                                                                        ivity                                                                             reac-                                                                     of  tion,               Catalyst                                              ethylene                                                                          H,                  diluent/               GHSV of                        (mol.                                                                             (Kcal.              catalyst                                                                              Reaction                                                                           Feed ratios                                                                             feed gases                                                                          C.sub.2 H.sub.6                                                                    Selectivity (%) for g.sup.-1                                                                          mol.sup.-1 of       Catalyst                                                                          ratio                                                                             temp.                                                                              (mol/mol) (cm.sup.3.g.sup.-1.                                                                 conversion                                                                            C.sub.3+4                                                                         C.sub.3+4    catalyst.                                                                         C.sub.2                                                                       H.sub.6             diluent                                                                           (v/v)                                                                             (°C.)                                                                       C.sub.2 H.sub.6 /O.sub.2                                                           C.sub.2 H.sub.6 /H.sub.2 O                                                         catalyst. h.sup.-1)                                                                 (%)  C.sub.2 H.sub.4                                                                  olefins                                                                           alkanes                                                                           CH.sub.4                                                                         CO CO.sub.2                                                                         h.sup.-1)                                                                         converted           __________________________________________________________________________    A) Improved supported catalyst C-2, prepared in Example-18                    SA  57.0                                                                              800  6.30 0.93 1,02,200                                                                            55.1 86.4                                                                             2.82                                                                              0.89                                                                              4.45                                                                             3.41                                                                             2.85                                                                             977 -5.52               5205    850  6.30 0.93 1,02,200                                                                            81.7 81.2                                                                             3.68                                                                              0.22                                                                              7.19                                                                             4.82                                                                             2.54                                                                             1362                                                                              +5.46                       800  7.30 0.95 1,02,200                                                                            59.3 83.7                                                                             1.94                                                                              0.65                                                                              6.81                                                                             4.55                                                                             2.24                                                                             1042                                                                              +1.54                       850  7.30 0.95 1,02,200                                                                            82.5 80.9                                                                             3.52                                                                              0.22                                                                              7.92                                                                             4.83                                                                             2.56                                                                             1401                                                                              +2.46                       800  8.00 0.96 1,02,200                                                                            51.2 85.2                                                                             1.40                                                                              1.01                                                                              4.34                                                                             5.64                                                                             2.35                                                                             918 +5.86               SA  65.8                                                                              800  6.30 1.82 1,50,650                                                                            46.0 83.1                                                                             2.30                                                                              1.91                                                                              3.90                                                                             6.20                                                                             2.83                                                                             1517                                                                              -6.33               5205    850  6.30 1.84 1,50,650                                                                            75.5 81.1                                                                             4.79                                                                              0.19                                                                              5.42                                                                             5.88                                                                             2.83                                                                             2438                                                                              +2.56                       800  7.30 1.85 1,52,700                                                                            48.9 85.6                                                                             2.02                                                                              1.15                                                                              4.11                                                                             5.01                                                                             2.11                                                                             1712                                                                              +0.99               B) Improved supported catalyst C-3, prepared in Example-19.                   SA   0.5                                                                              800  8.06 0.68 18,815                                                                              58.5 81.2                                                                             2.63                                                                              1.74                                                                              5.33                                                                             2.80                                                                             5.33                                                                             150 -0.40               5205    850  7.40 0.70 19,710                                                                              75.1 82.1                                                                             5.10                                                                              0.40                                                                              7.50                                                                             3.28                                                                             3.52                                                                             201 +6.66               __________________________________________________________________________

                                      TABLE 12                                    __________________________________________________________________________    Details of the preparation of improved supported catalyst in Example 21       to 25                                                                                       Example 21                                                                           Example 22                                                                           Example 23                                                                           Example 24                                                                           Example 25                          __________________________________________________________________________    Support used  SA 5205                                                                              SA 5205                                                                              SA 5205                                                                              SA 5205                                                                              SA 5205                             Shape and size of support                                                                   6 mm spheres                                                                         1 mm granules                                                                        2 mm granules                                                                        6 mm spheres                                                                         1 mm granules                       Precoating of the support with rare earth oxides                              Precursor compound of La                                                                    La-nitrate                                                                           La-nitrate                                                                           La-nitrate                                                                           La-nitrate                                                                           La-nitrate                          Precursor compound of R                                                                     Nd-nitrate                                                                           Nd-nitrate                                                                           Nd-nitrate                                                                           Sm-nitrate                                                                           Nd-nitrate                          R/La mole ratio                                                                             0.1    0.1    1.0    1.0    1.0                                 Decomposition temp. (°C.)                                                            500° C.                                                                       500° C.                                                                       500° C.                                                                       600° C.                                                                       500° C.                      Decomposition atmosphere                                                                    Air    Air    Air    Air    Air                                 Decomposition period (h)                                                                    4 h    4 h    3 h    4 h    4 h                                 Calcination temp. (°C.)                                                              930° C.                                                                       950° C.                                                                       900° C.                                                                       850° C.                                                                       900° C.                      Calcination atmosphere                                                                      Air    Air    Air    Air    Air                                 Calcination period (h)                                                                      4 h    4 h    5 h    10 h   6 h                                 Loading of rare earth                                                                       18.6%  17.6%  16.9%  15.7%  18.6%                               oxides, y (wt %)                                                              Deposition of alkaline earth metal oxides on precoated support                Precursor compound of Sr                                                                    Sr-nitrate                                                                           Sr-nitrate                                                                           Sr-nitrate                                                                           Sr-nitrate                                                                           Sr-nitrate                          Precursor compound of A                                                                     Mg-nitrate                                                                           Mg-nitrate                                                                           Mg-nitrate                                                                           Ca-nitrate                                                                           Mg-nitrate                          A/Sr mole ratio                                                                             0.1    1.0    0.1    0.1    1.0                                 Decomposition temp. (°C.)                                                            500° C.                                                                       500° C.                                                                       500° C.                                                                       450° C.                                                                       600° C.                      Decomposition atmosphere                                                                    Air    Air    Air    Air    Air                                 Decomposition period (h)                                                                    5 h    7 h    4 h    6 h    2 h                                 Calcination temp. (°C.)                                                              930° C.                                                                       900° C.                                                                       900° C.                                                                       950° C.                                                                       900° C.                      Calcination atmosphere                                                                      Air    Air    Air    Air    Air                                 Calcination period (h)                                                                      4 h    4 h    4 h    3 h    6 h                                 Loading of alkaline earth                                                                   26.4%  13.2%  10.0%  11.1%  12.4%                               oxides, x (wt %)                                                              Improved supported catalyst                                                                 C 1    C 2    C 3    C 4    C 5                                 produced                                                                      __________________________________________________________________________     C 1 = Mg.sub.0.1 SrO.sub.1.1 (26.4%)/Nd.sub.0.1 LaO.sub.1.65 (18.0%)/SA       5205;                                                                         C 2 = MgSrO.sub.2 (13.2%)/Nd.sub.0.1 LaO.sub.1.65 (17.6%)/SA 5205;            C 3 = Mg.sub.0.1 SrO.sub.1.1 (10.0%)/NdLaO.sub.3 (16.9%)/SA 5205;             C 4 = Ca.sub.0.1 SrO.sub.1.1 (11.1%)/SmLaO.sub.3 (15.7%)/SA 5205;             C 5 = MgSrO.sub.2 (12.4%)/NdLaO.sub.3 (18.6%)/SA 5205;                   

                                      TABLE 13                                    __________________________________________________________________________    Results on the oxidative conversion of methane to ethylene, ethane            or higher hydrocarbons (C.sub.2+ -hydrocarbons) over the improved             catalyst                                                                      prepared in Examples 21 to 25, with catalyst diluent/catalyst ratio of        1.0 (v/v), at different process conditions:                                                        GHSV of                CO/CO.sub.2                                                                        C.sub.2 H.sub.4 /C.sub.2                                                      H.sub.6                                                                             productivity                Reaction        feed gases                                                                           CH.sub.4        ratio                                                                              ratio in                                                                            (mmol ·                                                              g.sup.-1                                                                      ·             Catalyst                                                                           temp.                                                                              Feed ratios                                                                              (cm.sup.3 · g.sup.-1 ·                                             convertion                                                                         Selectivity (%)                                                                          in   products                                                                            catalyst                                                                      ·                                                                    h.sup.-1)              diluent                                                                            (°C.)                                                                       CH.sub.4 /O.sub.2                                                                  CH.sub.4 /H.sub.2 O                                                                 catalyst · h.sup.-1)                                                        (%)  C.sub.2                                                                           C.sub.2+                                                                         CO.sub.X                                                                          products                                                                           (mol/mol)                                                                           C.sub.2                                                                           C.sub.2            __________________________________________________________________________                                                               H.sub.4            A) Catalyst; Improved supported catalyst C-1 prepared in Example-21           SA 5285                                                                            805  17.8 10.0    56,500                                                                             11.9 82.6                                                                              87.2                                                                             12.8                                                                              0.34 0.42  107 32.1                    850  17.8 10.0    56,500                                                                             12.6 83.5                                                                              88.6                                                                             11.4                                                                              0.31 0.56  114 40.9                    850  20.8 10.0    56,500                                                                             10.7 84.9                                                                              90.2                                                                             9.8 0.30 0.50  108 33.3                    850  18.5 10.0  1,03,200                                                                             11.4 83.2                                                                              88.9                                                                             11.1                                                                              0.94 0.50  190 63.3                    850  4.0  10.0  1,03,200                                                                             39.4 80.1                                                                              65.2                                                                             34.8                                                                              0.33 1.10  311 163.0              B) Catalyst; Improved supported catalyst C-2 prepared in Example-22           Quartz                                                                             850  8.0  10.0  1,03,200                                                                             21.0 71.2                                                                              76.0                                                                             24.0                                                                              0.40 0.82  282 127.1                   850  16.0 10.0  1,03,200                                                                             12.3 81.6                                                                              86.1                                                                             13.9                                                                              0.69 0.53  199 68.9                    850  20.0 10.0  1,03,200                                                                             11.3 82.6                                                                              88.7                                                                             11.3                                                                              0.68 0.53  187 84.8               C) Catalyst; Improved supported catalyst C-3 prepared in Example-23           SA 5285                                                                            850  16.0 100.0 1,03,200                                                                             12.3 80.9                                                                              86.8                                                                             14.2                                                                              0.37 0.57  213 77.3                    850  24.0 100.0 1,03,200                                                                             10.0 85.8                                                                              90.1                                                                             9.8 0.39 0.47  188 60.1               D) Catalyst; Improved supported catalyst C-4 prepared in Example-24           SA 5285                                                                            850  16.0 19.0  1,03,200                                                                             11.4 82.8                                                                              87.6                                                                             12.4                                                                              0.55 0.54  187 65.6                    850  20.0 10.0  1,03,200                                                                             10.4 83.8                                                                              88.5                                                                             11.5                                                                              0.68 0.52  175 59.9               E) Catalyst; Improved supported catalyst C-5 prepared in Example-25           SA 5285                                                                            850  15.4 3.3   2,32,760                                                                             10.7 83.2                                                                              87.4                                                                             12.6                                                                              0.26 0.52  342 117.0                   850  15.4 3.3   2,32,760                                                                             12.3 81.6                                                                              84.8                                                                             15.2                                                                              0.70 0.32  336 144.8                   850  15.4 1.0   2,31,960                                                                             7.1  85.7                                                                              90.4                                                                             11.6                                                                              0.43 0.37  132 35.6               __________________________________________________________________________

                                      TABLE 14                                    __________________________________________________________________________    Results on the oxidative conversion of methane to ethylene, ethane            or higher hydrocarbons (C.sub.2+ -hydrocarbons) over the improved             catalyst                                                                      prepared in Examples 23 to 25, with catalyst diluent/catalyst ratio of        27.0 (v/v), at different process conditions:                                                GHSV of               CO/CO.sub.2                                                                        C.sub.2 H.sub.4 /C.sub.2                                                      H.sub.6                                                                             productivity                   Reaction      feed gases                                                                           CH.sub.4       ratio                                                                              ratio in                                                                            (mmol · g.sup.-1                                                     ·                     temp.                                                                              Feed ratios                                                                            (cm.sup.3 · g.sup.-1 ·                                             convertion                                                                         Selectivity (%)                                                                         in   products                                                                            catalyst ·                                                           h.sup.-1)                      (°C.)                                                                       CH.sub.4 /O.sub.2                                                                 CH.sub.4 /H.sub.2 O                                                                catalyst · h.sup.-1)                                                        (%)  C.sub.2                                                                          C.sub.2+                                                                          CO.sub.X                                                                         products                                                                           (mol/mol)                                                                           C.sub.2                                                                           C.sub.2 H.sub.4            __________________________________________________________________________    A) Catalyst; Improved supported catalyst C-3 prepared in Example-23           850  15.4                                                                              3.3  1,16,500                                                                             9.4  82.2                                                                             86.2                                                                              13.8                                                                             0.41 0.65  149 52.9                       880  15.4                                                                              3.3  1,16,500                                                                             11.3 81.2                                                                             85.3                                                                              14.7                                                                             0.37 0.83  177 80.3                       880  15.4                                                                              0.91 1,20,100                                                                             9.9  82.6                                                                             87.0                                                                              13.0                                                                             0.23 0.74  162 68.9                       B) Catalyst; Improved supported catalyst C-5 prepared in Example-; 23         850  15.4                                                                              3.3  1,16,500                                                                             11.5 81.1                                                                             85.7                                                                              14.3                                                                             0.44 0.68  180 72.9                       890  15.4                                                                              3.3  1,16,500                                                                             12.2 83.2                                                                             87.7                                                                              12.3                                                                             0.35 1.00  195 97.5                       890  21.5                                                                              3.3  1,16,500                                                                             10.2 84.0                                                                             88.0                                                                              12.0                                                                             0.49 1.00  167 83.5                       890  15.4                                                                              0.81 1,20,100                                                                             12.2 82.3                                                                             86.6                                                                              14.5                                                                             0.27 1.00  124 62.0                       __________________________________________________________________________

                                      TABLE 15                                    __________________________________________________________________________    Results on the oxidative conversion of natural gas (NG to ethylene            and higher hydrocarbons over the improved catalyst prepared in                Example-25, with different catalyst diluent/catalyst ratios at                different process conditions:                                                 Catalyst             GHSY of                                                                              Conversion         productivity                                                                          Net heat of            diluent/                                                                           Reaction                                                                           Feed ratios                                                                              feed gases                                                                           of carbon                                                                            Selectivity (%) for                                                                       of ethylene                                                                           reaction, K.sub.r      catalyst                                                                           temp.                                                                              (mol/mol)  (cm.sup.3 · g.sup.-1 ·                                             in NG     C.sub.2+ -                                                                             (mmol · g.sup.-1                                                     ·                                                                            (Kcal ·                                                              mol.sup.-1 of          ratio (v/v)                                                                        (°C.)                                                                       NG/O.sub.2                                                                         NG/H.sub.2 O                                                                        catalyst · h.sup.-1)                                                        (mol %)                                                                              C.sub.2 H.sub.4                                                                  olefins                                                                           CO                                                                              CO.sub.2                                                                         catalyst ·                                                           h.sup.-1)                                                                             carbon                 __________________________________________________________________________                                                           converted)             1.0  850  15.5 1.0   2,02,570                                                                             18.9   66.8                                                                             88.4                                                                              4.8                                                                             6.8                                                                              307     -3.46                  1.0  890  15.5 1.0   2,02,570                                                                             21.4   69.9                                                                             85.8                                                                              5.4                                                                             8.8                                                                              364     -4.96                  1.0  850  15.0 2.5   3,59,450                                                                             14.8   60.8                                                                             90.5                                                                              5.3                                                                             4.2                                                                              550     -2.54                  57.0 860  10.0 2.5   1,83,600                                                                             20.8   63.6                                                                             81.9                                                                              6.7                                                                             11.4                                                                             407     -16.31                 57.0 860  15.0 2.5   1,79,520                                                                             19.7   64.5                                                                             82.2                                                                              9.5                                                                             8.0                                                                              388     -4.64                  57.0 850  20.0 1.0   1,02,710                                                                             21.2   64.5                                                                             86.5                                                                              5.2                                                                             8.2                                                                              176     -4.40                  __________________________________________________________________________

We claim:
 1. An improved supported catalyst containing mixed strontiumand other alkaline earth oxides deposited on a sintered low surface areaporous catalyst carrier (or support) precoated with mixed lanthanum andother rare earth oxides, represented by the formula:

    A.sub.a SrO.sub.b (x)/R.sub.c LaO.sub.d (y)/S,

wherein, A is alkaline earth element selected from Be, Mg, Ca, Ba or amixture thereof; Sr is strontium; O is oxygen; R is rare earth elementselected from Ce, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu or amixture thereof; La is lanthanum; S is catalyst support selected fromsintered low surface area porous refractory inert solids comprising ofalumina, silica, silica-alumina, silicon carbide, zirconia, hafnia or amixture thereof; a is A/Sr mole ratio in the range of about 0.01 toabout 10; b is number of oxygen atoms needed to fulfill the valencerequirement of alkaline earth elements (A_(a) Sr); c is R/La mole ratioin the range of about 0.01 to about 10; d is number of oxygen atomsneeded to fulfill the valence requirement of rare earth elements, (R_(c)La); y is weight percent loading of rare earth oxides (R_(c) LaO_(d))precoated on the support in the range of about 0.5 wt % to about 50 wt %and x is wt % loading of alkaline earth oxides (A_(a) SrO_(b)) depositedon the precoated support in the range of about 0.4 wt % to about 40 wt%.
 2. A supported catalyst according to claim 1, wherein the support isin the form of granules (or aggregates) of size in the range of about0.1mm to about 8 mm or in the form of spheres, cylindrical pellets,rings, saddles or star of size or diameter in the range of about 1 mm toabout 15 mm, or in the form of monolith, and has surface area, porevolume and porosity in the range from about 0.001 m².g⁻¹ to about 5.0m².g⁻¹, about 0.02 cm³.g⁻¹ to about 0.6 cm³.g⁻¹ and about 5% to about75%, respectively.
 3. A process for the preparation of an improvedsupported catalyst, containing mixed strontium and other alkaline earthoxides deposited on a sintered low surface area porous catalyst carrier(or support) precoated with mixed lanthanum and other rare earth oxides,represented by the general formula:

    A.sub.a SrO.sub.b (x)/R.sub.c LaO.sub.d (y)/S,

wherein, A is alkaline earth element selected from Be, Mg, Ca, Ba or amixture thereof; Sr is strontium; O is oxygen; R is rare earth elementselected from Ce, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu or amixture thereof; La is lanthanum; S is catalyst support selected fromsintered low surface area porous refractory inert solids comprising ofalumina, silica, silica-alumina, silicon carbide, zirconia, hafnia or amixture thereof; a is A/Sr mole ratio in the range of about 0.01 toabout 10; b is number of oxygen atoms needed to fulfill the valencerequirement of alkaline earth elements (A_(a) Sr); c is R/La mole ratioin the range of about 0.01 to about 10; d is number of oxygen atomsneeded to fulfill the valence requirement of rare earth elements, (R_(c)La); y is weight percent loading of rare earth oxides (R_(c) LaO_(d))precoated on the support in the range of about 0.5 wt % to about 50 wt %and x is wt % loading of alkaline earth oxides (A_(a) SrO_(b)) depositedon the precoated support in the range of about 0.4 wt % to about 40 wt%, useful for the oxidative coupling of methane to higher hydrocarbons(i.e. C₂ +-hydrocarbons), oxidative conversion of natural gas toethylene and other lower olefins (propylene and butylenes) and oxidativeconversion of ethane or C₂ -C₄ alkanes to corresponding olefins, in thepresence of free oxygen, which comprises: (i) precoating of the surfaceof the support by the deposition of R_(c) LaO_(d) on it by impregnatingor coating the support with the mixed compounds of lanthanum and otherrare earth elements, represented by the general formulae: LaY_(g) andRY_(g), respectively, wherein La is lanthanum, R is rare earth elementselected from Ce, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu or amixture thereof, Y is an anion selected from nitrate, acetate, formate,oxalate, hydroxide, oxide and carbonate anion, g is number of Y neededto fulfill the valence requirement of lanthanum and other rare earthelements in their compounds, which on decomposition converts into oxideform, with R/La mole ratio, c, in the range of about 0.01 to about 10and in quantities sufficient to obtain a loading of R_(c) LaO_(d) onsupport in the range of about 0.5 wt % to about 50 wt %, by the knownincipient wetness impregnation, wet impregnation or coating methods,followed by drying the wet mass, and then decomposing the dried mass byheating it in air or inert gas or under vacuum at a temperature in therange of about 400° C. to about 700° C. for a period in the range ofabout 0.5 h to about 15 h and finally calcining it at a temperature inthe range of about 600° C. to about 1200° C. in air or inert gas orunder vacuum for a period in the range of about 0.2 h to about 20 h toobtain the support precoated with the rare earth oxides (R_(c) LaO_(d)),and (ii) deposition of A_(a) SrO_(b) on the surface of the precoatedsupport by impregnating or coating it with mixed compounds of strontiumand other alkaline earth elements, represented by the general formulae:SrX_(f) and AX_(f), respectively, wherein Sr is strontium, A is alkalineearth element selected from Be, Mg, Ca, Ba or a mixture thereof, X is ananion selected from nitrate, acetate, formate, oxalate, oxide, carbonateand hydroxide anion, f is a number of X needed to fulfill the valencerequirement of strontium and other alkaline earth elements in theircompounds, which on decomposition convert into the oxide form, with A/Srmole ratio, a, in the range of 0.01 to about 10 and in quantitiessufficient to obtain a loading of A_(a) SrO_(b) on the precoated supportin the range of about 0.4 wt % to about 40 wt % by the known incipientwetness impregnation, wet impregnation or coating methods, followed bydrying slowly the wet catalyst mass, and then decomposing the driedcatalyst mass by heating it in air or inert gas or under vacuum at atemperature in the range of about 400° C. to about 700° C. for a periodin the range of about 0.5 h to about 15 h and finally calcining it inair, inert gas or under vacuum at a temperature in the range of about600° C. to about 1200° C. for a period in the range of about 0.2 h toabout 20 h.
 4. A process according to claim 3, wherein the drying of thewet mass in stage (i) is effected by heating in air or under vacuum at atemperature of from about 40° to about 80° C. for from about 3.5 toabout 7 hours and then at a temperature of from about 90° to about 130°C. for from about 1 to 3 hours.
 5. A process according to claim 3,wherein the drying of the wet catalyst mass in stage (ii) is effected inair or under vacuum at a temperature of from about 40° to about 80° C.for from about 3.5 to about 7 hours and then at a temperature of fromabout 90° to about 130° C. for from about 1 to 3 hours.
 6. A process asclaimed in claim 3, wherein the support used in the catalyst preparationis in the form of granules of size in the range about 0.1 mm to about8.0 mm or in the form of spheres, cylindrical pellets, rings, saddles orstar of diameter or size in the range of about 1.0 mm to about 15 mm orin the form of monolith and has surface area, pore volume and porosityin the range of about 0.001 m².g⁻¹ to about 5.0 m².g⁻¹, about 0.02cm³.g⁻¹ to about 0.6 cm³.g⁻¹ and about 5% to about 75%, respectively. 7.A process as claimed in claim 3, wherein the alkaline earth element A isMg, Ca or a mixture thereof.
 8. A process as claimed in claim 3, whereinthe rare earth element R is Ce, Nd, Sm, Eu, Gd, Yb or a mixture thereof.9. A process as claimed in claim 3, wherein the A/Sr mole ratio, a,ranges from about 0.01 to about 1.0.
 10. A process as claimed in claim3, wherein the R/La mole ratio, c, ranges from about 0.01 to about 1.0.11. A process as claimed in claim 3, wherein the loading of alkalineearth oxides, x, ranges from about 2.5 wt % to about 25 wt %.
 12. Aprocess as claimed in claim 3, wherein the loading of rare earth oxides,y, ranges from about 3 wt % to about 30%.
 13. A process as claimed inclaim 3, wherein x anion is nitrate anion or acetate anion.
 14. Aprocess as claimed in claim 3, wherein Y anion is nitrate anion oracetate anion.
 15. A process as claimed in claim 3, wherein the methodof the precoating of support with the rare earth oxides and thedeposition of alkaline earth oxides on the precoated support is theincipient wetness impregnation method or the wet impregnation method.16. A process as claimed in claim 3, wherein the calcination temperatureof the precoated support in step (i) and supported catalyst in step (ii)ranges from about 800° C. to about 1000° C.
 17. A process as claimed inclaim 3, wherein the gas atmosphere used for the decomposition andcalcination of the precoated support in step (i) and supported catalystin step (ii) is air.